Router and methods using in-band link between managing processor and routing processor

ABSTRACT

A router for use in a network includes a scalable architecture and performs methods for implementing quality of service on a logical unit behind a network port; and for implementing storage virtualization. The architecture includes a managing processor, a supervising processor; and a plurality of routing processors coupled to a fabric. The managing processor has an in-band link to a routing processor. A routing processor receives a frame from the network, determines by parsing the frame, the protocol and logical unit number, and routes the frame to a queue according to a traffic class associated with the logical unit number in routing information prepared for the processors. An arbitration scheme empties the queue in accordance with a deficit round robin technique. If a routing processor detects the frame&#39;s destination is a virtual entity, and so is part of a virtual transaction, the router conducts a nonvirtual transaction in concert with the virtual transaction. The nonvirtual transaction accomplishes the intent of the virtual transaction but operates on an actual network port, for example, a storage device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional patent application of and claimspriority to U.S. patent application Ser. No. 10/120,266, filed on Oct.18, 2001, by William C. Terrell, et al.

FIELD OF THE INVENTION

[0002] Embodiments of the present invention relate to improved networkshaving routers that perform routing functions and to methods for routingnetwork traffic.

BACKGROUND OF THE INVENTION

[0003] In a conventional network, data is transferred between computersand peripherals to accomplish the data processing demands of thecomputers and peripherals. Demands for data to be transferred via thenetwork may arise in any particular computer or peripheral in a mannerunsynchronized with demands that arise on other computers andperipherals of the network. Data transfer to accomplish delivery isgenerally between respective ports of the computers and peripherals andmay pass through switches having ports as well. Such switches havenumerous ports and generally retransmit data (also called routingnetwork traffic) from one port to another according to addressinformation associated with the data to be transferred. A pair of portscommunicate via a link between the ports.

[0004] Demands generally vary widely in the amount of data to bedelivered over the network and the manner in which the delivery is to bemade. For example, some demands may be made for a relatively largeamount of data without regard to the order in which the data isdelivered via the network. Other demands may require that the data bedelivered in a particular order. Some demands may have no use for datathat is presented outside of an expected time for delivery. Otherdemands may be met at any time, though system efficiency may suffer ifdelivery is made outside of an expected time for delivery.

[0005] With a large number of network links, use of the network may beregulated to some extent by establishing a priority for each link. Inparticular, when attempts to meet demands result in delivery of data inbursts between pairs of computers and/or peripherals, networkperformance may exhibit several undesirable results. Network capacity(sometimes colloquially referred to as bandwidth) for servicing lowerpriority links may be unavailable. Delivery of data may be noticeablydelayed. More out of order deliveries may be made. And, service betweenports on particular links may be denied intermittently, causing queuesto fill and network capacity to be used for overhead messages regardingthe control of network traffic as opposed to actually routing thetraffic.

[0006] Traditional approaches to improving a network's ability todeliver data which would otherwise be delivered in bursts and todecreasing the likelihood of the undesirable results described abovehave focused on increasing network data transfer speed, increasing thedepth of queues for data awaiting processing before or after transfervia the network, and increasing the instruction processing speed forprocessors (e.g., per-port processors) that accomplish delivery over thenetwork. In a conventional architecture, each port may be implementedwith a processor and memory dedicated to servicing all forms of trafficfor that port.

[0007] In another known approach to solving some of the problemsdiscussed above, a traffic stream having a traffic profile is affectedby provisioning a facility for traffic conditioning as described inRequest For Comment “An Architecture for Differentiated Services,”RFC2475 by S. Blake of Torrent Networking Technologies. A trafficprofile is a set of desired temporal properties for a traffic stream(i.e., packet rate and burst size). A traffic stream is anadministratively significant set of microflows that traverse a pathsegment as selected by a particular classifier. Provisioning includesmapping traffic streams to per hop behaviors, and specifying methods oftraffic conditioning. Per hop behaviors are effected by shaping. Trafficconditioning is defined as classifying, metering, marking, shaping, anddropping packets. A microflow classifier selects packets (e.g., formarking) based on an arbitrary number of header fields including sourceaddress, destination address, protocol (e.g., IP), fields (e.g., DSfield in IP header), source port, and destination port. Marking isdefined (for IP) as setting the value of the DS field. Metering isdefined as measuring temporal properties of a traffic stream. Shaping isdelaying packets to conform a traffic stream to a desired trafficprofile. Shaping includes enqueueing a marked packet and holding thepacket in queue until transmitting the packet would not exceed a desiredtraffic profile. The basic architecture assumes that trafficconditioning functions are accomplished at each ingress and egress node(i.e., at each port of an edge node) of the network. According to afirst conventional hardware architecture, all traffic conditioningfunctions would be accomplished by a central processing unit (CPU)serving a group of ports at an ingress and egress node. Such a CPU wouldnot be capable of significant bandwidth. According to a secondconventional hardware architecture, each port of an edge node would beimplemented with a processor and memory dedicated to performing trafficconditioning functions by servicing all forms of traffic for that port.

[0008] A large portion of network traffic is associated with reading orwriting data storage media. The data delivery problems described aboveare evident in networks that provide shared access to data storagedevices. Managing data for improved access according to traditionalapproaches has included introducing servers between data storage devicesand the network. Such server technology impedes network traffic flow,and may facilitate unexpected denial of access or damage to data due tofailure mechanisms with a single point of failure.

[0009] Without the present invention, data delivery cannot be furtherimproved without unreasonably increasing the cost per port of thenetwork and the computers and peripherals that use the network.Increased costs stem from increased memory for queues and sophisticatedprocessing instructions to be executed by the port processors, fromincreased processing speed, and from circuits that operate at higherfrequencies to provide increased network data transfer speed. Thecomparatively high cost of circuits that operate at increased frequencystems from difficulties in designing such circuits and difficulties infabrication.

SUMMARY OF THE INVENTION

[0010] A router, in one embodiment of the present invention, routesframes in a network. The router includes means for participating as avirtual target in a virtual transaction initiated by an initiator of thenetwork and means for initiating a nonvirtual transaction with a targetof the network to accomplish an intent of the virtual transaction.

[0011] By analyzing at least a portion of a received frame, andpreparing an outbound frame back to the requester, a router operatingaccording to various aspects of the present invention provides a logicalinterface between the requester and resources. An additional outboundframe to a resource may be prepared by the router to fulfill therequest. A logical interface facilitates management of the resources forimproved efficiency and reliability of data transfers; and, supportsdemanding levels of quality of service as to order and timeliness ofdeliveries.

[0012] In another embodiment a router includes a processor that stores avirtual resource identifier and routes a frame that includes indicia ofa nonvirtual resource identifier. The nonvirtual resource identifier maybe determined by the processor with reference to an association betweenthe nonvirtual resource identifier and the virtual resource identifier.The association may be made by an administrating process andcommunicated to the processor as routing information.

[0013] A router, in another embodiment of the present invention,includes a processor that stores a resource identifier determined from afirst frame and routes a second frame in accordance with the resourceidentifier. For example, the second frame may be received withoutindication of the resource identifier and received after the first frameis received.

[0014] In another embodiment of the present invention, a router includesa processor that routes a frame in accordance with a policy value toimplement a quality of service. The policy value is determined at leastin part by parsing the frame to determine a resource identifier andrecalling an association of the policy value and indicia of the resourceidentifier. The association may be made by an administrating process andcommunicated to the processor as routing information.

[0015] By analyzing at least a portion of a received frame, andidentifying more than one field value, a router operating according tovarious aspects of the present invention selectively controls thequality of service as applied to particular data transfers and frameshaving particular sets of field values. Quality of service mayeffectively be controlled for a predetermined protocol and/orpredetermined group of resources. Quality of service may includespecifications regarding order and timeliness of deliveries, or in otherwords, bandwidth allocation, maximum delays, and reduction in networkcongestion. Statistics may be collected and analyzed for a subflow.

[0016] A router, in another embodiment of the present invention,includes a managing processor, a supervising processor, and a routingprocessor. The managing processor performs a proxy process that respondsto a control frame directed to a virtual entity. The supervisingprocessor performs a control process that responds to a control framedirected to the router. The routing processor routes data framesdirected respectively to virtual and to nonvirtual entities via thenetwork.

[0017] A router, in another embodiment of the present invention,includes two processors. The first processor performs a proxy processfor a virtual member of the network. The proxy process responds to acontrol frame having a first network port identifier. The virtual membercorresponds to at least one nonvirtual member or resource of thenetwork. The nonvirtual member responds to a data frame having a second(i.e., different) network port identifier. The second processor performsa routing process that routes frames having the first network portidentifier to the proxy process, routes frames having the second networkport identifier to the nonvirtual member, and on receiving a data framehaving the first network port identifier, routes a substitute data framehaving the second network port identifier. For example, data framesoriginally addressed to the virtual member are readdressed and routed toa corresponding nonvirtual (e.g., actual) member.

[0018] The modular architecture provided according to various aspects ofthe present invention permits scaling of the router design and scalingof the network, lowering the cost for competitive router products andimproving network maintenance.

[0019] A router, in another embodiment of the present invention, routesa frame received from a network. The router includes a routingprocessor. The routing processor includes: a frame processor, a parser,a plurality of queues, a submitter, and a memory circuit. The parserprepares a flow lookup in response to the frame received from thenetwork. The memory circuit performs a flow lookup and provides a resultas directed by the submitter and a first entry in a first queue, thefirst entry having been enqueued by the parser. The memory circuit alsoperforms a subflow lookup and provides a result as directed by thesubmitter and a second entry, the second entry having been enqueued in asecond queue by the frame processor in accordance with the result of theflow lookup. The frame processor routes the frame in accordance with theresult of the subflow lookup.

[0020] A router, in another embodiment of the present invention,includes: a plurality of physical ports, a managing processor, and atleast one routing circuit coupled to the manager by a first bus. Eachrouting circuit includes: a supervising processor, a memory, a secondbus, and a plurality of port logic circuits. The memory includes indiciaof a routing table. The memory is coupled to the supervising processorby the second bus. The plurality of port logic circuits is coupled tothe supervising processor by a third bus. Each port logic circuitprovides a multiplicity of the physical ports. Each port logic circuitis coupled to other port logic circuits for data transfer betweenphysical ports. At least one physical port of the plurality is coupledto the managing processor.

[0021] By providing in-band access to the managing processor,virtualization functions are less complex and more efficient. Wire speedvirtualization is facilitated.

[0022] A router, in another embodiment of the present invention,includes: a plurality of physical ports; a managing processor having afirst memory; and at least one routing circuit coupled to the managingprocessor by a first bus. Each routing circuit includes a supervisingprocessor and a plurality of port logic circuits. The supervisingprocessor has a second memory. Each routing circuit further includes athird memory. The third memory includes indicia of a routing table. Thethird memory is coupled to the supervising processor by a second bus.The plurality of port logic circuits are coupled to the supervisingprocessor by a third bus. Each port logic circuit provides amultiplicity of the physical ports. Each port logic circuit is coupledto other port logic circuits for data transfer between physical ports.Each port logic circuit has a frame processor that includes a respectivefourth memory. The managing processor updates the second memory via thefirst bus. The supervising processor updates the third memory and thefourth memory via the second bus.

[0023] By loading and updating routing information tailored toparticular frame processors and tailored to particular routingprocessors, the computational burden of performing virtualizationfunctions may be distributed among routers of a network.

[0024] A method, in another embodiment of the present invention, isperformed by a router for routing frames in a network. The routerincludes a plurality of network ports, a fabric, and a plurality ofrouting processors coupled between the fabric and the network ports.Each routing processor includes an ingress buffer for receiving framesfrom a network port and for transmitting frames to the fabric; an egressbuffer for receiving frames from the fabric and for transmitting framesto the network port; and a frame processor. On receiving from arequester a data frame directed to a virtual participant, the frameprocessor modifies the data frame in the ingress buffer for routing to anonvirtual participant. On receiving from the fabric a data frame notdirected to a nonvirtual requester, the frame processor modifies thedata frame in the egress buffer for routing to a nonvirtual requester.Further, the frame processor may, on receiving from the fabric a dataframe not directed to a nonvirtual requester for which the frameprocessor does not have sufficient modification information, route thedata frame via the fabric to another routing processor of the plurality.

[0025] A router, in another embodiment of the present invention,includes a first routing processor and a second routing processor and afabric. Each routing processor includes: an ingress buffer coupled to aninput port, an egress buffer coupled to an output port, a parser, and amemory that stores routing information. The ingress buffer is coupledbetween the input port and the fabric to transfer frames from theingress buffer to the fabric. The egress buffer is coupled between thefabric and the output port to transfer frames from the fabric to theoutput port. The first routing processor parses a frame received fromits input port to determine a virtual destination identifier, determinesa nonvirtual transaction identifier in response to the virtualdestination identifier, prepares a second frame having the nonvirtualtransaction identifier, and transmits the second frame to the fabric.The second routing processor receives the transmitted second frame fromthe fabric and transmits the second frame to its output port. The secondprocessor, on receiving a third frame on its input port parses the thirdframe to determine a nonvirtual transaction identifier, marks the thirdframe for modification, and transmits the third frame to the fabric. Thefirst processor receives the transmitted third frame from the fabric,parses the third frame to access the routing information from itsmemory, modifies the third frame in accordance with the accessed routinginformation, and transmits the modified frame from its output port.

[0026] By operating on frames in the ingress buffer and egress buffer, alower complexity router design results. For example, less memory isneeded for maintaining virtual context tables.

[0027] A router, in another embodiment of the present invention,includes a plurality of ports and a routing processor. The routingprocessor includes: at least a portion of a fabric, an ingress buffer,an egress buffer, The ingress buffer is coupled between the fabric and afirst port of the plurality to transfer frames from the fabric to thefirst port. The egress buffer includes a plurality of queues, anarbitrating circuit coupled between the egress buffer and the firstport, and a counter associated with each queue. Each counter has arespective current count. The arbitrating circuit (a) adds receivedgrants to a grant pool for the plurality of queues; (b) transfers aframe from a selected queue to the fabric when sufficient grants existin the grant pool; (c) decrements the grant pool in response to thetransfer; (d) adds transmitted frame size to the counter associated withthe selected queue; and tests whether the counter associated with theselected queue is greater than a threshold. If so, the arbitratingcircuit: (a) sets an overrun amount to the current count of the counterassociated with the selected queue; (b) resets the counter associatedwith the selected queue; (c) subtracts the overrun amount from a currentcount of each other counter; (d) clears all asserted stalled flags; and(e) stalls the selected queue.

[0028] A router, in another embodiment of the present invention,includes a plurality of routing processors each having at least aportion of a distributing circuit. Each distributing circuit portion hasa crossbar switch that completes a plurality of point-to-pointconnections between routing processors. The crossbar switch operates inresponse to at least one of: an input that indicates a number of routingprocessors that have been installed, and an input that indicates aposition of the routing processor among the number of routingprocessors. A second crossbar switch may provide a termination for apoint-to-point connection according to at least one of: an input thatindicates a number of routing processors that have been installed, andan input that indicates a position of the routing processor among thenumber of routing processors.

[0029] Combinations of the various aspects of the present inventionprovide solutions to the problems described in the background sectionand mitigate other problems. For example, stall and continuecapabilities on a subflow basis accommodate bursty network traffic fromvarious applications sharing a network link. Further, accommodatingquality of service differences (e.g., in the time or ordering of data)on a subflow basis better accommodates performance variations amongprocesses and storage functions in any member or within the network(e.g., an interswitch link). A router operating according to variousaspects of the present invention efficiently allocates bandwidth withoutcompletely stalling a low priority flow or unreasonably fragmenting ahigh priority flow. Routers that provide a logical resource interfaceprovide more efficient and more reliable networks for applicationservice providers and storage service providers, thereby lowering thecost of operating and lowering the cost of these services to theconsumer.

[0030] According to various aspects of the present invention,sophisticated network functions are accomplished without a generalpurpose processor per port. Such functions include, inter alia,mirroring, third party copy, arbitration based on subflows, subflowstalls, statistics gathering, provision of a logical resource interface,and maintaining caches in the router for read and write operations.

[0031] By maintaining one or more pointers to the original copy of asnapshot and possibly to revised portions of the snapshot, the time toinitially support use of a snapshot may be reduced and the interruptiondue to taking time to prepare a full copy of the snapshot may beavoided.

[0032] By maintaining a cache in the router, more efficient datatransfer to a member of the network results. Egress from the cache isprovided to meet the needs of the resource as opposed to the resourcebeing forced to accommodate operation of the network or operation ofanother network member.

[0033] By maintaining a cache in the router, a multicast write isaccomplished with fewer data transfers. More efficient network operationresults.

[0034] In a router architecture according to various aspects of thepresent invention, memory is provided where it can be effectively usedand the cost of router circuits can be decreased by avoiding largeamounts of memory that are infrequently accessed. Operations limit theneed to synchronize redundant copies of information in separate parallelprocessors within the router. Such an architecture supports framedisposition at the maximum rate on all ports and full mesh connectivityat wire speed. Routers based on scaling and reusable design (e.g., areconfigurable full mesh circuit) help control the overall router costand reduce dependency on higher cost processors and memory. Furthermore,routers with different quantities of ports may be economically assembledwith a greater reliance on common designs and subassemblies, loweringthe cost of manufacturing.

[0035] According to various aspects of the present invention, processorsthat are in the data path execute frame preparation functions withreference to commands and information prepared by processors that arenot in the data path. Such functions include, for example, accesscontrol from a centralized administration processor; providing securityfrom rogue processes (e.g., identifier translation tables (e.g., usedfor resource mapping or frame routing) are not directly accessible fromthe port interface); or gathering statistics on a subflow so thatcontrol decisions may be based on use of the network by a particulartype of process (e.g., Virtual Interface (VI) communication havingpriority over SCSI communication from the same port of the network) or aparticular type of storage device (e.g., streaming audio access havingpriority over data processing transactional file access). A managingprocessor in a router may filter statistics and more efficiently reportto an administrating processor for management of virtual resources.

[0036] An administrating processor updates the configuration (e.g.,routing tables) of several routers uniformly. An administrating processmay assign network port identifiers to be used for virtual members,virtual resources, and proxy processes. Proxy processes may receivecontrol frames for a virtual member or virtual resource.

[0037] As router products are developed with varying need forprocessing, the ratio of the various processors to the number of portsmay be economically scaled while continuing to benefit from theinvestment in circuit and firmware design. The following are but a fewexamples. The number of buses made active in the mesh may scale with thequantity and bandwidth of the ports. Port protocol support may bedownloaded to the processor(s) responsible for particular ports.Supervisory processing may scale with the quantity of ports in part dueto the bus interface between a plurality of port processing slices andthe supervisory processor(s). Managing processor(s) scale with thenumber of ports in part due to use of one or more in-band links to thesupervising processor(s). Processing responsibility scales with theamount of available memory due in part to the shared nature of memorybetween port logic circuits. RAID device control may be implemented atthe device cluster level from processor(s) in one or more routers orfrom processor(s) that is(are) part of a member. Multiple protocolcapability scales with different demands for different protocols.Multiple zone capability for load balancing scales by performance andextent of physical, logical, and virtual resources.

[0038] A router according to various aspects of the present inventiondetects in a virtual data frame a page boundary crossing, initiatesnonvirtual data frames to accomplish the operation intended, and routesthe nonvirtual data frames to corresponding nonvirtual storage. A pageboundary crossing occurs, for example, when reference is made in a dataframe to a portion of a virtual storage device, and the reference whenmapped to nonvirtual storage would include more than one page of one ormore nonvirtual storage devices.

[0039] By detecting page boundary crossings and initiating data frames,a requester may operate on a virtual resource without knowledge of thestructure and organization of the corresponding nonvirtual resource,simplifying such operations from the point of view of the requester.

BRIEF DESCRIPTION OF THE DRAWING

[0040] Embodiments of the present invention will now be furtherdescribed with reference to the drawing, wherein like designationsdenote like elements, and:

[0041]FIG. 1 is a functional block diagram of a system according tovarious aspects of the present invention;

[0042]FIG. 2 is a data flow diagram of processes in the system of FIG.1;

[0043]FIG. 3 is a data flow diagram of the administrating process ofFIG. 2;

[0044]FIG. 4 is a data flow diagram of the managing process of FIG. 2;

[0045]FIG. 5 is a data flow diagram of the supervising process of FIG.2;

[0046]FIG. 6 is a data flow diagram of the routing process of FIG. 2;

[0047]FIGS. 7, 8, 9, and 10 form a flow chart of a method for routingaccording to various aspects of the present invention;

[0048]FIG. 11 is a functional block diagram of a router of the system ofFIG. 1;

[0049]FIG. 12 is a functional block diagram of the supervising processorof FIG. 11;

[0050]FIG. 13 is a functional block diagram of the memory circuit ofFIG. 11;

[0051]FIG. 14 is a functional block diagram of the port logic circuit ofFIG. 11;

[0052]FIG. 15 is a functional block diagram of the descriptors of FIG.14;

[0053]FIG. 16 is a message sequence diagram for operations performed bythe system of FIG. 1;

[0054] FIGS. 17-20 form a flow chart of methods performed by router 102of FIG. 2;

[0055]FIG. 21 is a functional block diagram of a fabric having fivefabric nodes according to various aspects of the present invention;

[0056]FIG. 22 is a functional block diagram of the fabric of FIG. 20implemented with three fabric nodes;

[0057]FIG. 23 is a functional block diagram of the distributing circuitof FIG. 11; and

[0058]FIG. 24 is a message sequence diagram for operations performed bythe system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0059] A system according to various aspects of the present inventionmay include any computing environment supporting transfer of data amongcomputer systems via a communication network. Such a system, in oneimplementation, provides more efficient non-blocking delivery of data,improved utilization of bandwidth, a facility for managing networktraffic flows, subflows, and virtual flows, and higher quality ofservice. Data may be transferred between application programs beingexecuted by one or more of the computer systems, between an applicationprogram and a data storage device, or between one or more data storagedevices.

[0060] The network may be understood as a graph or a tree having networknodes. A communication network of the present invention includes atleast one computer system at each of several network nodes. Each networknode is coupled by a link from time to time for communication with othernetwork nodes. Each link includes conventional computer communicationtechnology at the physical layer and primitive layers of the typeincluding, for example, local area, wide area, dedicated telephone,wireless, and satellite services and including conventional datacommunication hardware and software at each network node. The popularcomputer networks known as storage area networks, intranets, theInternet, the World Wide Web, and the National InformationInfrastructure are examples of communication networks in which variousaspects of the present invention may be practiced. Network nodes aregenerally at physically separate locations and are generally suitablyidentified, for example, by a node name, node identifier, node address,a world wide identifier (WWPN), a uniform resource locator (URL), a namefrom a domain name system (DNS), or an Internet Protocol address (IP).

[0061] Data transfer at the lowest level occurs via a link betweenports, nominally a requesting port and a participating port, where arequesting port requests a data transfer and the participating porteither supplies the data (e.g., a read) or receives the data beingtransferred (e.g., a write). A port includes a physical implementationfor common signaling between ports (e.g., any circuitry suitable for thetransfer media); and a logical implementation (e.g., any combination offirmware and software). Cooperation between ports occurs in accordancewith a physical protocol (e.g., signals and their characteristics) and alogical protocol (e.g., one or more layers of application programinterfaces). The physical and logical implementations and protocolstogether constitute a port by which other software can manage, amongother things, how to obtain the data to be supplied to the port and whatto do with the data obtained from the port. A port may communicate usingseveral protocols. Frames according to a first protocol may beencapsulated (i.e., become the payload) in frames according to anotherprotocol. Ports of a router according to various aspects of the presentinvention may support, for example, combinations of Fibre Channel (FC)Protocol (FCP), Internet Protocol (IP), based IEEE 802.3 Ethernetprotocol, Small Computer Systems Interface (SCSI) Parallel Interface,Serial Bus Protocol, IEEE 1384 (Fire wire), SSA SCSI-3 Protocol,Scheduled Transfer, and Virtual Interface (VI).

[0062] A network node may include one or more ports. Multiple ports at anetwork node may be serviced as a group (e.g., a hunt group) to serve anupper level process with higher band width, to provide fail-overcapability, or to serve multiple parallel processes. Network nodeidentifiers (e.g., port identifiers) facilitate requesting (e.g.,initiating) and participating in a data transfer (e.g., performing as atarget or as a virtual target).

[0063] A group of ports may provide data transfer functionstransparently. For example, a bridge, located between a requester and aparticipant, may receive requests in a first protocol (e.g., notunderstood by the participant) and provide a corresponding request tothe participant in a second protocol (e.g., not understood by therequester). Further, a router, located anywhere in the network, mayserve as a hub for several links; each link being served by one or moreports. Such a router routes network traffic between a requester (havinga requesting port) and a participant (having a participating port)without either the requester or the participant having knowledge of theport identifiers of the ports of the router. The router transferstraffic between its ports in accordance with a routing table thatdefines communication paths through the router. The routing table may bespecified by a network technician, by an administrator as discussedbelow, or may be determined by the router as a result of communicationwith other routers to which it is linked. A router according to variousaspects of the present invention may function as a gateway receivingframes at an input port according to a first protocol and forwardingframes to an output port that (a) encapsulate the input payload; (b)strip the encapsulation of an input frame and forward the payload to theoutput port; or (c) use frames of the second protocol to conduct thefunction intended by the first protocol (e.g., data transfer with avirtual destination or with a logical destination; or a VirtualInterface transaction to a SCSI transaction).

[0064] A system according to various aspects of the present inventionincludes a communication network and numerous computer systems. Any ofthe computer systems that are currently members of the communicationnetwork, may transfer data to any other computer systems that aremembers of the communication network (or will be at a suitable futuretime) via links through routers. For example, system 100 of FIGS. 1-6,11-14, and 23 includes communication network 101 (i.e., network 101) andmembers 110-117. Network 101 includes a link to each member:respectively links 150-158 to members 110-117. Network 101 also includesrouters 102-105. The quantity, configuration, and arrangement ofmembers, links, and routers in system 100 is merely illustrative and anynumber, configuration, and arrangement may be used in practice of thevarious aspects of the present invention.

[0065] Practice of variations of the present invention is independent ofwhether any particular link is maintained continuously, as in adedicated line, or is maintained for a suitable duration. Members,links, and routers may each incorporate multiple units and be organizedto provide redundancy or fail-over capacity to avoid a single failurefrom disrupting communication.

[0066] System administration includes establishing and maintainingrouter configuration for some or all routers of a network as theutilization of the network changes, as link reliability changes, and asthe network grows or shrinks in number of links, routers, and members.Information for manual or dynamic network administration may becollected and reported by routers of the network. Administration may beaccomplished by use of one or more workstations (e.g., for a humanoperator) or servers (e.g., for administration directed by process(es)running on the servers). Network 101 includes administration subsystem109 having port 106. Link 107 supports communication betweenadministration subsystem 109 and any router of network 101, particularlyconnecting port 106 to port 108 of router 102. Ports 106 and 108 andlink 107 may be identical in structure and function to links and portsdescribed above with reference to routers and members. In an alternateimplementation, administration may be accomplished by any suitablemember.

[0067] System administration may include management of network topologyand may include management of virtualization. Virtualization includesthe designation (e.g., mapping) of a nonvirtual member or nonvirtualresource (e.g., a nonvirtual entity) to be used in place of anyreference to a virtual member or to a virtual resource (e.g., a virtualentity), the communication of that designation to suitable routers, andthe use of that designation in routing packets. Routers according tovarious aspects of the present invention may perform the communicationand use of designations that are defined by system administration.

[0068] A member of a network is a computer system that communicates viaa link as described above and either operates, inter alia, to requestdata transfer or to participate in data transfer via the link. Somemembers may provide a resource to network 101 so that all members of thenetwork may share the capability of the resource. For example, members110-119 may include all or any part of the structure and functionsdescribed below with reference to members 115-116. Members 115-116 arecapable of requesting data from any other member 110-117 orparticipating in data transfer with any other member 110-117 and viceversa.

[0069] Any member may include a subnetwork. A subnetwork includes anysubsystem that employs ports connected to network 101 for communicationgenerally between any member of network 101 and any subnetwork member(e.g., a resource) that is not directly connected to network 101. Theinterface between network 101 and such a subsystem may provideredundancy, fail-over, multiple or expanded use of network ports, accesscontrols, security (e.g., functions of a conventional firewall),protocol conversion (e.g., functions of a bridge), and/or priority flowcontrols (e.g., functions of a router as discussed herein). For example,member 115 includes subnetwork 170 having ports 165 and 166 connected tonetwork 101 via links 155 and 156 respectively, a port interface 171, aresource interface 172, a controller 173 servicing interfaces 171 and172, a plurality of resources 174 that includes a processing resource175, and a storage resource 177. Port interface 171, resource interface172, and controller 173 may cooperate as a server 178. The plurality ofresources 174 may include zero or more processing devices (e.g.,computers, servers, or workstations) and zero or more storage devices(e.g., disks, tapes, media handlers, or RAID systems).

[0070] Port interface 171 performs suitable port interface functions(e.g., signaling protocols) as described herein and is exemplary ofports 160-168 respectively of members 110-117. Port interface 171 isconfigured, directed, and controlled by controller 173. Any conventionalstatus and command interface signaling may couple port interface 171 andcontroller 173. Resource interface 172 performs suitable interfacefunctions (e.g., signaling protocols) to accomplish any conventionalnetwork functions for and among resources via subnetwork 170. Inalternate implementations, interfaces 171 and 172 may be integrated asone interface, may operate in the absence of a controller 173, and/ormay be integrated with one or more resources. Port interface 171 andresource interface 172 communicate over line 176 (e.g., a bus or alink).

[0071] Controller 173 accomplishes all conventional protocol functionsnot already implemented in port interface 171 and resource interface172. Controller 173 may include memory used, for example, forprogrammable operations of controller 173, data buffering, statefulcontrol of interfaces 171 and 172, and subnetwork communication.Controller 173 communicates with the plurality of resources 174 viasubnetwork 170. Subnetwork 170 may include any conventional logical andphysical organization. As shown, each resource 175 and 177 communicateswith resource interface 172 via a dedicated link. Communication betweenresources and from resources to ports 165 and 166 is accomplished by thecooperation of interfaces 171, 172, and controller 173. Controller 173may perform processing of the type known as Random Array of IndependentDisks (RAID) for one or more storage devices 177. Controller 173 mayperform routing and priority functions for fail-over and load sharingamong processing devices (e.g., functioning as an application serviceprovider) and/or analogous functions among storage devices (e.g.,functioning as a storage service provider).

[0072] A resource provides any capability used with data communication.For example, processing device 175 and storage device 177 may includeconventional computers, array processors, peripherals, personalcomputers, workstations, telecommunications equipment, disk drives, diskdrive arrays, tape drives, tape drive arrays, printers, scanners, videodisplays and cameras, audio equipment, and measurement instrumentation.Generally, devices 175 and 177 and to some extent controller 173 providefunctions described above as a resource to network 101.

[0073] Subnetwork 170 may be any conventional network (e.g., a LAN, SCSInetwork, Fibre Channel network, Integrated Drive Electronics (IDE)network, or a star interface to just a bunch of disks (JBOD)).Communication to and from resources 174 may refer to any suitable deviceidentifiers (e.g., World-Wide Identifiers (WWPNs), logical unit numbers(LUNs), or device addresses).

[0074] A router includes any mechanism that provides a logicalcommunication facility between a requester and one or more participants.The facility may be dedicated (e.g., independent of all othercommunication through the router) or shared (e.g., time multiplexed).When communication is accomplished by separating data into frames (alsocalled packets), frames may be passed through the facility in order, outof order, with or without regard to a time period specified fortransfer, repeated, or dropped. If the facility is of the typeconventionally known as non-blocking, no frame that properly enters therouter will be dropped. A facility that is non-blocking at full capacitywill drop no frames while all its ports operate indefinitely at maximumcontinuous communication link capacity. A router according to variousaspects of the present invention provides a virtual communicationfacility alone or in cooperation with other routers.

[0075] A frame that enters a router at a given port may exit the routerat any one or more ports including the port from which it entered, asdirected by router configuration (e.g., static paths and/or dynamicrouting tables). For example, router 102 provides non-blockingcommunication among ports 108, 130-133 respectively supporting links107, 150 and 121-123; router 103 provides non-blocking communicationamong ports 134-137 respectively supporting links 121, 151, 152, and124; router 104 provides non-blocking communication among ports 138-143respectively supporting links 122, 124, 153-155, and 125; and router 105provides non-blocking communication among ports 144-148 respectivelysupporting links 123, 125, and 156-158.

[0076] A router may serve as a core router or as an edge router. Routers102-103 are illustrated as edge routers because they serve links tomembers 110-112 that are outside of boundary 102. Boundary 102 may bedesignated for security purposes or represent a physical or politicaldivide. Routers 104-105 are illustrated as core routers because allports serve links to members within boundary 102 or serve other routersof network 101. In an alternate network, the ports of a core routerserve no members, only other routers. Analysis of frames for purposes ofdetermining a classification and consequently designating theeffectivity of a suitable policy value may occur at an edge router asopposed to a core router. Effectivity may be implemented, for example,by marking a frame, setting a preference bit, specifying a priorityvalue, setting a preemption bit, or identifying a suitable output queuethat is serviced in a manner that is consistent with a desired qualityof service. Core routers may be programmed to pass traffic without suchanalysis. A router may act as an edge router as to some ports (e.g.,ports 140 and 141 of router 104) and as a core router as to other ports(e.g., 138-139 and 142-143 of router 104).

[0077] Interswitch links 121-125 may employ any conventional protocol,including a protocol different from the protocol used between a routerand a member. For example, frames leaving a router's port onto aninterswitch link may include additional information that may be removedbefore the frame is passed on a non-interswitch link. Further, thequality of service (QoS) provided by a router's port to an interswitchlink may be better than the quality of service provided by a router'sport to a non-interswitch link.

[0078] Preferably, all of a router's ports have identical port physicalimplementations, for example, for convenience of installation andmaintenance of network 101 as other routers and links are added tonetwork 101. A frame routed on an interswitch link may be marked (at aningress edge router) as discussed above for effecting a policy and suchmarking may be removed (at an egress edge router).

[0079] Communication among members and resources, according to variousaspects of the present invention, is supported by a system architecturethat facilitates expansion and reliability. Expansion includes, interalia, adding physical assemblies to the system to support additionalports, links, and/or processing capacity as well as to support redundantand fail-over capabilities. Reliability is further enhanced by, intera/ia, dividing processing responsibility to avoid processing andcommunication bottlenecks, and by modular and reusable procedural, data,and hardware structures.

[0080] A system architecture is a plan by which system functions aremade the responsibility of particular processes for efficientperformance of system functions and for efficient communication amongprocesses. The system architecture is systematically applied asimplementations of the system are developed and expanded. For example,system architecture 200 of FIGS. 2-6 includes administration subsystem109, network 101, and router 102 comprising managing, supervising, androuting processes. Implementations of router 102 provide one or moreprocessors for executing these processes. Systems employing architecture200 solve the problems discussed above (e.g., provide qualities ofservice), expand and contract without disruption of services, andexhibit extraordinary reliability.

[0081] An administration subsystem includes any computer having a portfor communication via a link to network 101 and a processor thatperforms an administrating process. For example, administrationsubsystem 106 of FIGS. 1 and 2 may include one or more servers and/orworkstations that provide a user interface and a port 106, coupled bylink 107 to port 108 of router 102.

[0082] An administrating process provides routing information to anyrouter of a network and receives reports from any router of the network.The routing information provided to a router from an administratingprocess may define alternative paths through the network that a routermay choose on a frame by frame basis. When a frame identifies adestination to which it is to be routed, each router of the network, asa consequence of receiving routing information from an administratingprocess or from another router, may have one or more alternative pathsthat it may use to route the frame successfully. The router is generallyfree to make the choice of a particular path in accordance with routinginformation and other information, including current traffic conditions.Administrating includes assisting a human operator to develop suitablerouting information for any number of routers of the network. To thatend, the administrating process may also obtain or be automaticallyprovided with information describing current conditions of the network.For example, administrating process 202 receives reports from router 102via network links 107 and provides routing information (e.g., paths) vianetwork link 107 to router 102. By coupling the administrating processto the router via network links, any suitable number and locations ofadministrating processes and administration subsystems may be used toaccomplish reliable access to any or all routers of network 101.Consequently, all administrating functions are scalable to thecomplexity of network 101 as network 101 may expand (e.g., as thequantity of routers to be administered by a particular administrationsubsystem may increase).

[0083] In one implementation system administration includes networkmanagement and virtualization management functions that may be performedindependently by different operators. In addition, routers of thenetwork may include conventional routers (e.g., that do not recognizevirtual members and virtual resources) and routers according to variousaspects of the present invention (e.g., that recognize a packet that isdestined for a virtual member or a virtual resource). Virtualizationmanagement includes communicating the designation of a nonvirtual memberor resource to each router that is responsible for implementing anonvirtual transaction corresponding to (e.g., in place of) a virtualtransaction. The router receiving such communication is responsible forrouting packets of the virtual transaction and of the nonvirtualtransaction in accordance with routing information as discussed above.

[0084] A router, according to various aspects of the present inventionincludes scalable processes and scalable interfaces for communicationbetween processes. Consequently, routers of any suitable complexity(e.g., number and speed of ports, number of protocols supported, andextent of frame analysis) may be implemented in accordance witharchitecture 200. For example, router 102 includes managing process 204,supervising process 206, and routing process 208. In operation, managingprocess 204 receives routing information via network 101 and providesrouting information to supervising process 206 via bus 210; supervisingprocess 206 stores routing information in memory 211 from which routingprocess 208 retrieves it; and, routing process 208, routes framesthrough links 214 and 216 to network 101 with reference to routinginformation recalled from memory 211. Frames received from network 101are generally handled by routing process 208 in one of three ways:routing at least the payload of the same or corresponding frames tonetwork links via fabric 213 and ports 216, routing at least the payloadof the same or corresponding frames to managing process 204 via ports201 and 214, and passing at least the payload of the same orcorresponding frames to supervising process 206 via bus 212.

[0085] Particular advantages are realized in a system according tovarious aspects of system architecture 200. For example, by providingbuses 210 and 212 as physical entities, processes 204, 206 and 208 maybe hosted by independent processors (e.g., processors having accessprivileges over particular resources or separately packagedmicroprocessors). Consequently, each process 204, 206 and 208 may behosted (e.g., provided with suitable resources) in scale with thecomplexity of functions performed by router 102. Significant economiesresult including economies related to modular circuit, firmware, andsoftware design techniques. For example, one or more managing processes204 may communicate on bus 210 with any number of supervising processes206. One or more supervising processes 206 may communicate on bus 212and by virtue of shared access to memory 211 with any number of routingprocesses 208. One or more routing processes 208 may communicate withnetwork 101 via any number of ports 216 (e.g., conveying frames to anyadministrating subsystem and any network member) and communicate withany number of managing processes 204 via ports 201-214. In an alternateimplementation, buses 210 and 212 may be a common entity. In yet anotheralternate implementation, processes 204, 206 and 208 may be performed byfewer than three processors (e.g., one processor or one array processor)and bus communication may be replaced with conventional interprocesscommunication (e.g., software interrupts, semaphores, common buffers,and multithreading).

[0086] An administrating process includes any process that provides auser interface to a human operator for the purpose of determiningrouting information (e.g., for virtualization management, or networkmanagement) to be used in routers of a network and that providesinformation regarding network utilization. For example, administratingprocess 202 of FIG. 3 includes edit paths process 302, obtain reportsprocess 304, manage link loads process 310, display link utilizationprocess 312, and port I/O (i.e., input/output) process 306. Routinginformation may be presented, stored, and communicated in any suitableform.

[0087] Edit paths process 302 creates and revises routing information,automatically and in response to input by a human system operator.Routing information, according to various aspects of the presentinvention, may include any combination of descriptions including: a setof alternate paths through the network, an association of a virtualmember and at least one of a nonvirtual member and a nonvirtualresource, and an association of a virtual resource and at least onenonvirtual resource. Each path and association may be defined to includeseveral links and policy values. Each link may be identified as alogical entity or as a physical entity.

[0088] A logical entity (e.g., a logical link, a logical resource, or alogical member) may correspond from time to time with one or morephysical entities. By referring to a logical entity, the correspondencebetween the logical entity and any particular physical entity (orentities) may be determined dynamically, or in accordance withinformation that is not available at the time that the reference to thelogical entity is made. For example, a reference to a logical entityneed not be revised in light of the addition or removal of redundantphysical entities. Consequently, system 100 may expand or portions ofsystem 100 may fail and the reference to the logical entity remainsvalid (e.g., does not require amendment to continue particular networkfunctions). At the physical level, a router that has received a frame onone of its ports either routes or drops the frame. Routing includesdetermining (not necessarily unambiguously) at least one physical outputport to which the frame may be directed. If no such output port can bedetermined (or the only such output port is not available), the frame issaid to be dropped. Dropping a frame (e.g., for lack of informationsufficient to route the frame) accomplishes a denial of access to themember or resource intended to receive the frame.

[0089] Routing of frames between members (and resources) is somewhatanalogous to sending a letter through the postal system. The letteroriginally bears the address that the sender believes is the currentaddress of the intended recipient. For example, the sender may live inOhio and may address a letter to a corporate headquarters in Georgiarequesting a copy of the latest specialty catalog. The sender need nothave any knowledge of the street addresses of the post offices or thenames of their internal departments that may be involved. Suppose thatthe corporation has moved its headquarters to Florida and has filed withthe Georgia post office a notice of change of address. When the letteris routed from the point of deposit into the postal system in Ohio tothe post office in Georgia, the postal workers in Georgia may place theoriginal letter in a surrounding envelope and address the outer envelopeto Florida. The corporation may recognize from the outer envelope orotherwise that the letter is requesting a specialty catalog. Thecorporation may then enclose the outer envelope and its entire contentsin a further enclosing envelope and apply the address of a particularcatalog fulfillment center in Indiana; then redeposit it in the postalsystem. At the fulfillment center in Indiana, all envelopes may bediscarded and the catalog shipped to the requester's Ohio address givenin the letter.

[0090] When a router operating according to various aspects of thepresent invention determines that the frame that entered the router musthave an additional address, a frame that encloses (and thereby includes)the received frame may be prepared and routed. This is analogous toenclosing the letter in an outer envelope as discussed above. Forexample an in-bound edge router may enclose the frame and an out-boundedge router may discard the outer frame and pass merely the inner frame.Alternately, a router operating according to various aspects of thepresent invention may prepare a frame that contains the payload of theoriginal frame and a different address than originally received. This isanalogous to covering an address on a letter with a sticker that bears aforwarding address. Generally, a frame bears at least one destinationidentifier; an address being one form of an identifier as discussedabove. The several identifiers that may be encountered in operation ofsystem 100 are outlined briefly in Table 1 tracing the routing of arequest for data to be supplied by a resource (e.g., a request from SORTprocess 181 of member 116 for file CITIES from member 115. TABLE 1Source or Network Destination Entity Context Services Identifiers RoleMember User's Upper level User's handle, Requester (e.g., 116) process(e.g., protocol API record number SORT 181) Member Operating OperatingOperating system (e.g., system API system handle, 182) filename MemberLogical unit Device Path, logical unit abstraction driver number, blockmanager API address range Member Logical unit Device Logical unit (e.g.,as driver API number, page supported by number, sector device drivernumber 183) Member Logical port Port API Logical port Requester, (e.g.,167) identifier Source Member Physical port Signals Physical portidentifier Router Physical port Signals Physical port Ingress identifierRouter Logical port Router input Logical port (e.g., 147) port logicidentifier Router Virtual unit Router Virtual unit virtualizationnumber, page API number, sector number Router Logical unit Router Path,logical unit abstraction management number, block routing logic addressrange Router Logical unit Router Logical unit logic number, page number,sector number Router Logical port Router Logical port (e.g., 146) outputidentifier port logic Router Physical port Signals Physical port Egressidentifier Member Physical port Signals Physical port (e.g., 115)identifier Member Logical port Port API Logical port Participant, (e.g.,166) identifier Destination Member Logical unit Device Logical unitdriver API number, page number, sector number Member Logical unit DevicePath, logical unit abstraction driver number, block manager addressrange API (e.g., controller 173) Member Operating Operating Operatingsystem system API system handle, filename (e.g., CITIES file on disk177) Member Data entity Upper level User's handle, protocol API recordnumber

[0091] Routing information may be stored in any conventional databasesuch as paths database 303. In one implementation, paths database 303includes for each router a data structure (e.g., one or more files)having records, each record comprising a data structure having fieldsfor a destination identifier as specified in a received frame and one ormore of a list of alternate logical or physical ports of the router towhich the frame may be routed. Table 2 lists several records of pathsdatabase 303 describing sets of paths for routers 102, 104, and 105. Thereference numbers in Table 2 identify ports shown in FIG. 1. In recordscorresponding to rows of Table 2, reference numbers would be replacedwith logical port identifiers. TABLE 2 Router Output port Destination atwhich of the port as the router at indicated in frame which the theframe was frame was received received received Comment 165 105 145 Uselink 125 to router 104. 165 105 144 If link 125 is busy or down, uselink 123 to router 102. 166 105 146 Use link 156 to destination. 166 105145 If link 156 is busy or down, use link 125 to router 104. 165 104 142Use link 155 to destination. 165 102 132 Use link 122 to router 104.

[0092] Routing information may include associations of policy values andport identifiers (e.g., for network ports such as 165 and/or for routerports such as 145). Generally a policy value includes any value thatspecifies (e.g., directly, or indirectly by identifying anotherspecification) access permissions, desired quality of service, priority,connection type (e.g., connection oriented, connectionless) class ofservice, traffic class, or other transaction controls to be implementedbefore or during routing. Policy values include any control valuesdefined by a protocol including the identification of the protocol(e.g., SCSI and version number). For example, a Fibre Channel headerincludes a CS_CTL field that describes a class of service havingfunctional specifications that assure a particular quality of service.

[0093] When routing information is being prepared by edit maps process302, any representation of a port may be used (e.g., a name from a nameserver, an index or pointer into a list of names, a mnemonic, an icon, aworld wide port name WWPN). Routing information may be entered by asystem operator in any conventional manner including “point-and-click”,“drag-and-drop”, identification of a group of ports as equivalent (e.g.,ports 165 and 166 may be identified as functionally equivalent as tomember 115), or identification of a group of members of the network orof one or more subnetworks that are to be considered as a zone for acommon purpose such as specifying policy values.

[0094] In one implementation according to various aspects of the presentinvention, routing information between physical entities is developed byrouters 102-105 without user intervention according to methods performedby routers 102-105 that (a) identify port capabilities of all portscoupled to each port of a router; (b) advertise port identifiers toother routers via interswitch links; and (c) maintain routinginformation (e.g., further identification and advertising) when changesin port connections are detected. In such an implementation, the virtualports, virtual members, and virtual resources (with suitable policyvalues) might not be discovered by routers 102-105 and are developed byan administrating process with user input.

[0095] Routing information (e.g., paths database 303) may be stored andmaintained in a relational database. In one implementation, policyvalues are associated with group names, group names are associated withidentifiers of members, and zone names are associated with identifiersof resources (processes and devices). A zone name may be used todescribe a virtual member or a virtual resource. Further, group/zonetuples of group name, zone name, and policy values may be derived ormaintained in such a database. Still further, member/resource tuples ofmember identifier, resource identifier, and policy values may be derivedor maintained. In an alternate implementation, the derivation ofmember/resource tuples is accomplished by managing process 204 based onmaps received from administrating process 202.

[0096] Routers of network 101 may gather information useful for anyportion of administrating process 202. Obtain reports process 304 mayuse any suitable technique to obtain such information from routers102-105. For example, obtain reports process 304 may poll routers ofnetwork 101 by sending a frame containing a command (e.g., a fabriccontrol command or link service request). Routers 102-105 may providesuch information in any suitable form from which obtain reports process304 formats one or more entries in reports database 308. Obtain reportsprocess 304 may, for example, use commands of the Simple NetworkManagement Protocol (SNMP) to read any register or region of memory in arouter 102-105. For example, routers 102-105 may provide lists of ports,image data, maps, and current configuration information from whichadministrating process 202 may develop new, expanded, or revised paths.

[0097] A method for preparing a map according to various aspects of thepresent invention includes in any order: requesting member identifiersand resource identifiers from routers of the network; associating eachmember identifier to a group of members; associating each resourceidentifier to a zone of resources; associating a path and a policy valueto at least one of the group and the zone; determining port identifiersassociated with the path; and communicating the policy value to eachrouter of the network having at least one port identified to the path.In alternate implementations, the group and/or zone layer of indirectionmay be omitted so that path and policy values are associated directlywith member identifiers and resource identifiers.

[0098] A method for preparing a map that enables routing to virtualentities (e.g., virtual members, virtual resources) includes in anyorder: (a) providing a name for each of any number of virtual membersand/or virtual resources; (b) associating one or more portions ofnonvirtual members and/or nonvirtual resources with each of the names;and (c) communicating each association to at least one router on eachpath used to communicate between a nonvirtual member and either of avirtual member or a virtual resource. The method may also includeassigning a network port identifier to each virtual member or virtualresource. When a resource is divisible into fungible units (e.g.,identically functioning units of storage or processing such as sectoraddresses or object references), the method may further includeassociating a unit of a nonvirtual resource to the name or to a portionof a virtual resource. For example, a sector of a named virtual resourcemay be associated with a sector of a nonvirtual resource.

[0099] Policy values may include access control values (e.g.,identifiers of members or resources permitted to access other members orresources). Access controls may be associated with nonvirtual andvirtual members and resources.

[0100] A method for facilitating network traffic may include the stepsof: (a) preparing a map to facilitate routing of frames referring tovirtual entities; (b) providing policy values associated with virtualentities; and (c) communicating the identifiers of virtual entities onlyto members or resources permitted to access them. Communication of theidentifiers may be by selectively advertising.

[0101] A definition for implementing a database for use by edit pathsprocess 302 and storage of routing information in paths database 303 isdescribed in Table 3. TABLE 3 FILE (or list) and associated fields or arecord (or entry) Description GROUP/POLICY A named group may serve as alogical construct used to group_name describe a set of policy values.Group names may be policy_value associated with policy values inmany-to-many relationships. In other words, several policy values may beassociated with a group name and the group name serve as an indicationof the combination of policy values. Requesters (e.g., initiators) maybe identified to groups as opposed to zones. MEMBER/GROUP A member, asidentified by any suitable identifier (e.g., IP member_identifieraddress, or WWPN), may be associated with a group name to group_nameindicate that the policy values of the group are to be associated withall network traffic involving the member. Members may be associated withgroups in many-to-many relationships. An administration system operatormay designate a member_identifier (e.g., an unused name) as adesignation of one or more actual members. Such a member_identifier isherein called an identifier of a virtual member. ZONE/POLICY A namedzone may serve as a logical construct used to zone_name describe a setof policy values to be applied to resources and policy_value membersthat are part of the zone. Zone names may be associated with policyvalues in many-to-many relationships. Participants (e.g., targets) maybe identified to zones as opposed to groups. RESOURCE/ZONE A resource,as identified by any suitable identifier (e.g., IP resource_identifieraddress, WWPN; for a process, an object reference or zone_name referenceof the type used with CORBA), may be associated if virtual, theassociated with a zone name to indicate that the policy values of thenonvirtual resource identifier, zone are to be associated with allnetwork traffic involving and (if applicable) virtual unit to theresource. Resources may be associated with zones in nonvirtual unitcrossreferences many-to-many relationships. An administration system(e.g., page/sector table or object operator may designate aresource_identifier (e.g., an unused reference crossreferences) name) asa designation of one or more actual resources of one or more actualmembers. Such a member_identifier is herein called an identifier of avirtual resource. A virtual resource may be associated with an actual orvirtual member. A virtual member may have virtual resources. MEMBER/ZONEA member and all resources of the member (if any) may bemember_identifier associated with a zone as discussed above. zone_nameif virtual, associated nonvirtual member identifier PATH/PORT A namedpath may serve as a logical construct for developing path_name routinginformation. Typically two ports define the extremessource_port_identifier of a path: the port of a requester (e.g., asource) that is destination_port_identifier associated with a member orresource, and the port of a router_identifier participant (e.g., adestination) member or resource. An output_port_identifieradministrating process may have no knowledge of the routers and theiroutput ports that may be involved in alternate paths — leaving amanaging process in a router to obtain, integrate, and dynamicallymaintain such information, supplementing the definition of a path.Nevertheless, identifiers and ports may be associated to a path name tothe extent that an administrating process may suitably designatealternate routes or paths between groups, zones, members, and resources.MEMBER/PORT A port identifier may be a logical or physical reference toa member_identifier particular port. During member login to a port of aparticular router_identifier router, the member identifier and portidentifier may be port_identifier associated, for example, in a nameserver. A port identifier for a virtual member may be designated by anoperator of the administration subsystem. RESOURCE/PORT The identity ofa resource may be associated with a port of a resource_identifierparticular router, as discussed above. A port identifier for arouter_identifier virtual member may be designated by an operator of theport_identifier administration subsystem. GROUP/ZONE/PATH Theassociation of a path to a group, a zone, or both, provides group_namean association of policy values to the path. When policy zone_namevalues as defined for the group and the zone conflict, any path_namesuitable negotiation of policy values may occur to result inpolicy_values policy values to be used for the path. Integration ofpolicy values may follow predetermined hierarchical rules maintained byan administrating process (e.g., edit paths process 302) or by amanaging process. Negotiation may be accomplished dynamically during alogin sequence. Resulting policy values associated with a path form thebasis for routing tables. MAP A map may include policy values to beimplemented for any router_identifier or every router of the network. Asegmented map or an source_port_identifier overall map may be derivedfrom the records discussed destination_port_identifier above. In animplementation where routers develop routing policy_values informationwithout operator input, one or more of the fields crossreferences fordescribed here may be omitted. implementing routing for virtual entitiesROUTING TABLE A routing table for a particular router may be prepared asan source_port_identifier excerpt from a MAP. The operator of the systemdestination_port_identifier administration subsystem may determine whichrouters will policy_values use crossreferences for routing virtualentities. According to crossreferences for various aspects of thepresent invention, the readdressing of a implementing routing forvirtual frame that originally designated a virtual entity is entitiesaccomplished at any one router along a path; other routers along thatpath need not have access to crossreferences implementing routing forthat virtual entity. In one implementation, the burden of processingvirtual routing is distributed among routers of network 101. In animplementation where routers develop routing information withoutoperator input, one or more of the fields described here may be omitted.IMAGE An image may include information for routing, supervising,routing_table_entries and managing including data (e.g., constants,tables, routing_process_data configuration information), and programs(e.g., downloaded routing_process_programs subroutines for use by arouting processor to perform routing supervising_process_data of aparticular type of frame of a particular protocol issupervising_process_programs recognized by a parser). In a networkcapable of determining managing_process_data paths for actual membersand resources, the image may be managing_process_programs limited toinformation regarding routing of virtual

[0102] A port input/output process provides an application programinterface (API) by which an application program may send and receiveframes for communication (e.g., command, control, status, and datainterchange) with other application programs, resources, and members ofthe network. For example, port I/O process 306 conducts all lower levelprotocols to permit administration process 202 to have access toinformation stored in routers and members of system 100. Port I/Oprocess 306 provides an API to obtain reports process 304 and to managelink loads process 312.

[0103] Links are subject to traffic that consumes available capacity ofthe link herein called a link load. The link load may be quantified ashaving frame rate, delays between frames, bursts of immediatelysucceeding frames, burst length, delays between bursts, and relatedderived quantities (e.g., maxima, minima, averages, counts, rates,variances) during a suitable duration of measurement or monitoring.Management of a link load at the level of system administration involvestransferring routing information from time to time to routers of network101; and, providing information to assist development of routinginformation. For example, manage link loads process 310 sends portionsof paths database 303 that apply to a particular router (e.g., rows 1-4of Table 2) as an update to the particular router (e.g., router 105) inany manner suitable for limiting the disruption of ongoing networkservices. Updates may occur when a router logs into the fabric and atany suitable time thereafter. Manage link loads process 310 may requestparticular reports from obtain reports process 304 or may make reportsfrom database 308 according to any conventional query.

[0104] The loads on various links over time and/or as related to one ormore members constitute link utilization. Link utilization may bedisplayed in system 100 in any conventional aggregated or sorted manner.For example, display link utilization process 312 reads reports 308 andpresents link utilization to the system operator via a graphical userinterface. The system operator may analyze displays presented by displaylink utilization process 312 to determine that improved systemperformance may result if portions of paths database 303 are edited.Display link utilization process 312 may request particular reports fromobtain reports process 304 or may make reports from database 308according to any conventional query.

[0105] In each router of system 100 (e.g., 102), a managing processaccepts paths sent in frames to the router from an administratingprocess and provides reports in frames to the administrating process.For example, managing process 204 accepts paths as sent by manage linkloads process 310 and provides reports from time to time to obtainreports process 304. Due in part to the scalable architecture discussedabove, each router may receive updates from any administrating processand provide reports as requested or automatically to any administratingprocess. A managing process, according to various aspects of the presentinvention, includes any process that performs one or more of thefollowing operations: providing routing information to one or moresupervising processes; obtaining from one or more supervising processesinformation for reports as discussed above; governing operation of oneor more supervising processes to assure policy values are effected on aparticular link; serving as a proxy for one or more members in anycommunication (e.g., for virtualization); operating a cache to providean up to date redundancy of all or a portion of data stored at a member;and operating a cache to maintain a mirror storage resource as a copy ofanother storage resource. For example, managing process 204 includesport I/O process 402, LAN I/O process 404, manage configuration process406, map store 408, image store 409, obtain and supply reports process410, reports 412, load balance process 414, launch proxy for memberprocess 416, any number of proxy for member processes 418, proxy state420, cache agent process 422, cache 424, and mirror agent process 426.

[0106] Port I/O process 402 performs functions analogous to port I/Oprocess 306, discussed above.

[0107] LAN I/O process 404 provides an API for processes within router102 to communicate via bus 210. Bus 210 may be of the type known as alocal area network (LAN), for example, including IP over IEEE 802.3Ethernet for supporting, among other functions, an interprocess protocolof the promulgated by the Object Management Group as Common ObjectRequest Broker Architecture (CORBA).

[0108] Managing configuration for a router, according to various aspectsof the present invention, includes establishing initial values andupdates of values stored in any memory device of the router. Forexample, manage configuration process 406 may receive configurationinformation (not shown) and routing information (e.g., paths) fromadministrating process 202 by SNMP communication, in frames, or in filetransfers (e.g., comprising data in XML). Manage configuration process406 determines router specific routing and configuration information,and stores received and derived information in map store 408 and inimage store 409. Manage configuration process 406 determinesconfiguration values that may be suitably tailored for one or moresupervising processes 206. Configuration information may be derived inaccordance with the establishment or termination of a proxy for amember, discussed below. Configuration information may also be derivedin accordance with a result of load balancing, discussed below.

[0109] Routing information (e.g., paths, and associations implementingvirtualization) may be received having references to logicalidentifiers. Mange configuration process 406 may refer to a name service(e.g., domain name service) to replace logical identifiers with physicalidentifiers and store results (e.g., maps) in map store 408. Maps in mapstore 408 may be used to develop routing information for particularrouting processes. Routing information particular to a routing processmay be combined with other data (configuration information, data, andprograms) to form an image for transfer to a routing process.

[0110] Image store 409 is organized for convenient access by manageconfiguration process 406. Manage configuration process 406 may accessimage store 409 for reading configuration information, forming a propermessage for the protocol on bus 210 (e.g., determining an address of asupervising process 206 for receipt of the configuration information);and for storing configuration information that may be reported bysupervising processes from time to time via bus 210. Manageconfiguration process 406 includes watchdog timers that notice when aconfiguration of a supervising process has changed, and when such aprocess is no longer responding. Manage configuration process 406 mayexecute a reset on any supervising process (or processor) in an attemptto re-establish proper operation of a supervising process (orprocessor). Image store 409 may contain a description of the state ofeach supervising process 206 managed by manage configuration process406.

[0111] Supervising processes are managed to coordinate operation of arouter in an initial configuration, a power-on configuration (e.g.,persistent from a recent power-off configuration), and an expandedconfiguration (e.g., additional ports and supervising processes addedwithout disrupting current routing functions). Configuration informationto be stored in a memory device of the router includes codes (e.g.,flags, identifications, controls, and interrupt settings) for commandregisters (herein called command/status registers (CSRs)), programs forinstruction stores (e.g., microcode for a state machine, nativeinstructions for a processor, or statements for an interpreter), andvariables and data for main memory (e.g., semiconductor and/or diskstorage for variables, tables, and related data for random access memoryor content addressable memory). These memory devices may be volatile ornonvolatile (herein generally called erasable programmable memory(EPM)). Consequently, manage configuration process 406 may conduct aseries of download operations via LAN I/O process 404 (in cooperationwith LAN I/O process 502) and may receive status and acknowledgementsfrom LAN I/O process 404.

[0112] A managing process may obtain reports from a routing process; andthe managing process may provide reports to an administrating process.Reports may be specified as to content and format by the administratingprocess and/or the managing process. According to various aspects of thepresent invention, communication of reports between all such processesutilizes network frames. The consuming process for any report mayrequest the report specifically each time it is desired, or specify asubscription for the report to be fulfilled without further interventionby the consuming process. The providing process may produce reports onlywhen requested (e.g., when polled), or may produce reports in responseto lapse of a timer or on the occurrence of an event (e.g., an abnormalcondition, or a condition requiring information and processing powerfrom a managing or administrating process). Any conventionalcommunication protocol may be used to implement the request/reply orsubscription mechanisms. A variety of protocols may be used for avariety of reports. For example, obtain and supply reports process 410sends requests via ports 214 (FIG. 2) conforming to SNMP to routingprocess 208 and routing process 208 sends replies via ports 214 toobtain and supply reports process 410 in conformance to SNMP. Moreparticularly, port I/O process 402 parses incoming frames and deliversframes identified as SNMP to obtain and supply reports process 410.Obtain and supply reports process 410 sends reports from managingprocess 204 via ports 201 to administrating process 202 via ports 107using network frames as discussed above.

[0113] According to various aspects of the present invention, a managingprocess may designate in a map a type of frame and an address recognizedby the managing process so that a routing process, operating accordingto the map, that receives a frame of the designated type will route theframe to the managing process. Generally, frames are of two types: thoseinvolving data transfer; and otherwise, those involving control and/orstatus. For example, manage configuration process 406 may specify in amap that control frames of particular protocols (e.g., controls forvirtual participants) are to be routed to a network port that isrecognized by the parser of port I/O process 402. Such a map, passed tomap 211 as discussed above, is used by routing process 208.

[0114] Part of a map may designate nonvirtual members (or resources)that are to be used when reference is made to virtual members (orresources). Each virtual member may accomplish the data processing anddata communication functions of a member by obtaining the services ofone or more nonvirtual (i.e., actual) members, nonvirtual resources, orportions thereof. The designation of nonvirtual resources to a virtualmember may be specified by administrating process 202 and communicatedto managing process 204 as part of a map. Operations on a virtual member(e.g., by control frames or data frames) may be accomplished on aphysical device (e.g., member 110, or device 175 or 177), may beaccomplished on a logical device (e.g., member 115 corresponding toresources on subnetwork 170), or on another virtual device as long as anonvirtual device can be identified for the operations (e.g., nocircular references or undefined virtual identifiers).

[0115] Launch proxy for member process 416 includes any process thatanalyzes frames and prepares replies to accomplish any of the following:(a) establish a virtual member; (b) identify any or all existing virtualmembers; and (c) perform for a virtual member any action appropriate fora nonvirtual member (e.g., respond to any control frame). Communicationwith a virtual member, in accordance with various aspects of the presentinvention achieves the effect that the requesting member is unaware thatthe request was accomplished by a proxy as opposed to a nonvirtualmember. These determinations and replies may be accomplished usingprotocol analysis and communication techniques similar in some respectsto conventional parsers and port I/O processes suitably modified forlaunching and cooperating with one or more proxy processes. Launching aproxy includes maintaining a list of operating proxy processes,dedicating resources (e.g., memory in a managing processor) for use bythe proxy, determining an identifier for the proxy, updating routinginformation to enable communication with the proxy, and preparing toaccept status and error condition messages that may originate with or bea consequence of the proxy. For example, when port I/O process 402determines that a frame is a request to identify or to establish avirtual member, port I/O process passes the frame (or relatedinformation) to launch proxy process 416. Launch proxy process 416responds by identifying an existing proxy or launching a new proxy asdiscussed above.

[0116] A proxy process includes any process that receives frames in afirst transaction and that prepares frames directed to a nonvirtualmember or resource in a second transaction. The first and secondtransactions may be in the same protocol or in different protocols. Thefirst and second transactions may be separate in time or may overlap intime. A nonvirtual member or resource has state according to theprotocol used to communicate with the nonvirtual member or resource. Aproxy process makes virtual state visible to the user of the virtualmember or resource (e.g., in response to a control frame). For example,each proxy process 418 operates as if it were a nonvirtual member havingstate according to the protocol used by the user of the virtual member.The state of the nonvirtual member and the virtual state as made visibleby the proxy to the user of the virtual member may differ. When theprotocol used with the nonvirtual member is identical to the protocolused with the virtual member, the respective states may correspond. Evenso, these states may differ, for example, because of temporaldifferences between the conduct of the first transaction and the secondtransaction.

[0117] Proxy state includes any data structure for maintaining the stateof the virtual member (or resource) and the state of the correspondingnonvirtual member (or resource). For example, proxy state 420 includes aconventional data base stored in any suitable memory (e.g., acombination of semiconductor and disk memory devices). Proxy state 420may comprise any suitable organization of records with fields asdescribed in Table 3A. TABLE 3A Field Description on-line Describeswhether the device (a member or a resource) is available for login tothe network; logging-in Describes whether the device is currentlyparticipating in a log-in scenario; device Describes whether the deviceis currently assigned a valid port available which may be specified in atransaction; accessible Describes for a storage device what portions ofthe storage pages device are ready (or will be ready) for immediateaccess due in part to the structure (e.g., a portion of the storagemedium proximate to the read/write head) and operation (e.g., seek timesto other cylinders, or to other portions of streaming tape) of thestorage device.

[0118] A cache agent process includes any process that maintains data ina relatively faster access memory so that reference to a relativelyslower access memory may be avoided. The capacity of the faster accessmemory is generally subject to limitations on the amount, type, ororganization of data stored therein. A cache agent process receivesrequests for data bearing suitable identification of the desired data,examines the cache first and if the desired data is not there, obtainsthe data and possibly stores the data in the cache to facilitate futurereference to at least part of the same data. If the data is in thecache, the cache agent process provides the data in response to therequest and may note that the data has been accessed. The cache agentmay determine whether to retain data in the cache in response tonotations as to its having been accessed (e.g., time of last access,total number of accesses in a period of time, and/or identity of therequester for which access was made or destination to which the data wasprovided). For example, cache agent 422 receives requests from port I/Oprocess 402, performs the functions of a cache agent as discussed aboveby accessing cache 424, and directs port I/O process 402 to reply withdata as requested to be sent to the requester.

[0119] A mirror agent process includes any process that maintains morethan one copy of particular data. A second copy of data (also called themirror) when read at any time must provide the same result as readingthe primary copy of data (the data that is being mirrored). The primarydata is expected to be subject to change by being written. To properlymirror primary data that has been written, the write to the second copymust be made prior to a read of that portion of the second copy thatwould be affected by the write. According to various aspects of thepresent invention, a mirror agent process may prepare and maintain thesecond copy without initially preparing a complete copy of the primarydata. In other words, the second copy may at any instant of time (a) beempty, (b) contain primarily or exclusively a copy of the data that hasbeen written to the primary copy, or (c) contain primarily orexclusively a copy of the data that has been read from the primary copy.By delaying copying unused portions of the primary copy to the secondcopy, network traffic may be more effectively used for other networkfunctions. For example, mirror agent process 426 receives requests fromport I/O process 402 to maintain one or more copies of identified data,performs the functions of a mirror agent as discussed above by accessingcache 424, and directs port I/O process 402 to perform reads of theprimary copy and writes to the second copy to maintain the second copyas discussed above.

[0120] A cache includes any data structure for facilitating access todata as discussed above. For example, cache 424 includes a conventionaldata base stored in any suitable memory (e.g., a combination ofsemiconductor and disk memory devices).

[0121] Each routing process may communicate with a managing process 204or its components (406, 414, 410, 416, 418, 422, 426) using one or morenetwork port identifiers (e.g., destination addresses). Such a networkport identifier may be a predefined address, an address reserved to therouter, a world wide port name, or a so-called well known address.Network port identifiers may be used by routing processes and byadministrating processes to communicate with managing processes. Arouting process generally communicates primarily or exclusively with themanaging process in the same router as the routing process.Communicating by use of a network port identifier of network 101 is alsocalled “in-band” communication. By contrast, networks 210 and 212, forexample, do not represent “in-band” communication.

[0122] A supervising process, according to various aspects of thepresent invention communicates with one or more managing processes 204via LAN 210; and, communicates with any number of routing processes 208via at least one of bus 212 and shared memory 211 as discussed above.Such communication maintains a current map 211 for use by each routingprocess and accomplishes link services for the links maintained by eachrouting process. For example, supervising process 206 includes LAN I/Oprocess 502, image store 503, update images process 504, get linkservice request 506, put link service reply 507, control fabric process508, log 510, serve names process 512, namestore 514, broadcast process516, and group store 518.

[0123] Supervising process 206 cooperates with manage configurationprocess 406 to receive routing information. LAN I/O process 404 providesrouting information according to a protocol followed also by LAN I/Oprocess 502 for receipt and acknowledgement of routing information. LANI/O process 502 may also provide indications that supervising process206 is operating properly via the cooperation of LAN I/O processes 502and 404. LAN I/O process 502 analyzes routing information that has beenreceived and stores routing information in image store 503.

[0124] Image store 503 is organized for convenient access by LAN I/Oprocess 502 and update images process 504. Image store may includecodes, programs for instruction stores, variables, data, and routinginformation, as discussed above with reference to image store 408.Update images process 504 may access image store 503 for readingconfiguration information, forming a proper message for the protocol onbus 212 (e.g., determining an address of a routing processor for receiptof the configuration information), and for storing configurationinformation that may be reported by routing processes from time to timevia bus 212. Update images process 504 includes watchdog timers thatnotice when a configuration of a routing process has changed, and whensuch a process is no longer responding. Update images process 504 mayexecute a reset on any routing process (or processor) in an attempt tore-establish proper operation of a routing process (or processor). Imagestore 503 may contain a description of the state of each routing processmanaged by update routing memory process 406. Update images process 504reads image data from image store 503 and stores image data for accessby routing processes as discussed above with reference to map 211. Namestore 514, map 211, and group store 518 may receive initial values andbe updated from image store 503. For example, identifiers and policyvalues (including access control values) for virtual members and virtualresources may be stored in name store 514 to be advertised or providedon request by serve names process 512 (e.g., in one implementation onlypermitted access is facilitated by selectively providing virtualidentifiers in accordance with access control values). Image data mayinclude data to be referenced by, and instructions to be performed byone or more routing processes. Update images process 504 monitorsrouting processes 208 in any conventional manner and initializes andupdates image data in map 211 at any suitable time or interval.

[0125] A link service request is a request sent by a member or resourceof network 101 that can be accomplished with reference to datamaintained by a router. Generally, a link service request is completedwith a link service reply. Requests for data transfer between membersare generally not considered link service requests. Link servicerequests are generally defined by a protocol of network 101. When router102 supports more than one protocol, one or more supervising processesmay coexist in router 102, for example, one process for each protocol.For example, get link service request process 506 and put link servicerequest 507 perform conventional interprocess communication betweensupervising process 206 and one or more routing processes 208. Linkservice requests may be processed in any conventional manner. Forexample, get link service request process 506 distinguishes fabriccontrol requests, name service requests, and broadcast requests androutes respective requests to control fabric process 508, serve namesprocess 512, and broadcast process 516. Each of these processes preparesa suitable reply for use by put link service reply process 507. Put linkservice reply process 507 provides the reply to the routing process thatmade the request. Table 4 describes representative link service requestsand processing. All of the processes described in Table 4 may invokeaction by put link service reply process 507 to generate a suitablereply to each link service request. A reply may describe resultconditions or error conditions concerning the link service request. Aproxy process 418 performed by managing process 204 may initiate anycontrol frame for a virtual member or resource (e.g., initiate a linkservice request, log-in a virtual member, or designate a quality ofservice for a virtual resource). TABLE 4 Link Service Request/ReplyDescription of Processing Abort a transaction Control fabric process 508revises log 510 and notifies statistics gathering processes (if any) sothat the transaction identified in the link service request isinterrupted without completing the request of that transaction. Remove aconnection Control fabric process 508 revises log 510 and notifiesstatistics gathering process (if any) so that the path identified in thelink service request is interrupted. Such a path may be a dedicatedpath. Ports involved along the path (or paths) are freed for generaluse. Log-in Control fabric process 508 revises log 510 and may notifyrouting process 208 to report current members of the network toadministrating process 202. Serve names process 512 revises name store514 with a new or unused name for the device. A port is identified tothe device that desires to become a member of the network via the port.Log-out Control fabric process 508 revises log 510 and may notifyrouting process 208 to report current members of the network toadministrating process 202. Serve names process 512 revises name store514 to disassociate the name from the device that was a member. A portis disassociated from the device to remove the member from the network.Implement a quality of Control fabric process 508 revises log 510 andmap 211 from which service routing process provides the quality ofservice specified in the link service request. Implement a bufferControl fabric process 508 revises map 211 from which routing processcredit or grant 208 dedicates or frees buffer space for frame handling.When managing process 204 provides a proxy process implicated in thislink service request, control fabric process 508 cooperates withmanaging process 204 to implement the requested credit or grant.Implement a group Broadcast process 516 revises group store 518 and map211 from address which routing process 208 operates to broadcast ormulticast frames to more than one destination.

[0126] A routing process generally routes frames by analyzing each framereceived from a port, selecting suitable routing information, andproviding at least the received payload in the same or a correspondingframe to an output port. A routing process provides access to membersand resources as requested by a member (or resource) that has suitablepermission (e.g., via an access control list), provides quality ofservice according to suitable policy values, and maintains transactionswith physical, logical, and virtual entities. A routing process alsoobtains and reports statistics. For example, routing process 208includes statistics store 601, report status and errors process 602,pass link service request process 603, supervisor queue 604, field linkservice reply process 606, route frame to fabric process 608, manageoutput queues process 610, manage egress queues 612, egress buffer 614,ingress buffer 616, flow process 618, pass to proxy process 620, routingtable 622, subflow process 624, context table 626, virtual flow process628, virtual context table 630, page table 632, sector table 634,virtual port identifier table 636.

[0127] Routing process 208 provides reports 214, 201 to managing process204. Information reported describes traffic through router 102. Eachrouting process 208 may accumulate counts of the quantity of framessatisfying a variety of criteria. These counts and data derived withreference to the counts is stored in statistics store 601. Counts mayaccumulate over a period of time fixed, specified by supervising process206 or dynamically determined by routing process 208. Data may includeone or more of the following computations: average, ratio, net change,rate of change, variance, standard deviation, and binary results from acomparison of a current value of data to a threshold that may be fixed,specified by supervising process 206 or dynamically determined byrouting process 208. Access to statistics may be indexed in anyconventional manner.

[0128] The subject of a count or derivative may be limited to a physicalport, logical port, virtual port, flow, subflow, virtual flow, member,or resource identified for example, by analysis of one or more fields ina frame (e.g., pattern matching by a parser circuit).

[0129] Report status and errors process 602 reads statistics 601 ordetermines status, configuration, or error conditions of routing process208 and prepares a suitable report. Report preparation may be automatic(e.g., on occurrence of an error or lapse of a reporting time period) orpolled (e.g., in response to a request 201, 214 from managing process204).

[0130] Pass link service request process 603 formats informationrecalled from statistics store 601 or received from report status anderrors process 602. Pass link service request process 603 also formatsinformation received by flow process 618 so that any portion of a linkservice request frame may be provided to supervising process 206. Passlink service request process 603 stores the formatted information insupervisor queue 604.

[0131] Supervisor queue 604 serves as a buffer between pass link servicerequest process 603 and field link service reply process 606.Supervising process 206 may access supervisor queue 604 in each ofseveral routing processes as described above with reference to bus 212.By buffering link service requests, (a) supervising process 206 mayimplement priorities for the execution of link service requests (in anorder other than as requested) and processing of reports (in an orderother than as polled or as available); (b) pass link service requestprocess 603 may specify and revise priorities among outstanding items inqueue 604, (c) supervising process 206 may delay processing ofparticular link service requests or reports, (d) results of processingby supervising process may be noted in queue 604, and (e) field linkservice reply process 606 may act on replies from queue 604 in any orderand at any suitable intervals, allowing route frame to fabric process608 to implemented priorities without loss of data.

[0132] Field link service reply process 606 reads replies fromsupervisor queue 604 (entered into the queue in response to a linkservice request or report as discussed above). Reading may be responsiveto thresholds to avoid backlog in queue 604, may be upon lapse of a timeperiod (fixed, specified, or determined as discussed above), or may beupon request from route frame to fabric process 608. Field link servicereply process 606 prepares a suitable link service reply frame that mayinclude data read from or derived with reference to queue 604 and passesthe frame to route frame to fabric process 608.

[0133] A fabric is a mechanism that provides access to data amongnumerous source processes and destination processes. In oneimplementation a fabric comprises a multiported memory allowing anynumber of source processes to write into the memory and any number ofdestination processes to read from the memory. In another implementationthe fabric comprises a network that makes a copy of data from a sourcebuffer into one or more destination buffers. Source and destinationbuffers may then be implemented as memories with much simpler accessfunctions: a source buffer is read by the network and written by onesource process; and a destination buffer is written by the network andread by one destination process. Network processes at each of severaldestination buffers may implement multicasting or broadcasting bystoring a copy from a multicast or broadcast source that is madeavailable to all destination network processes. For example fabric 213provides communication among any suitable number of routing processes208 each having respective processes 610 and 612. Fabric 213 mayimplement communication with any combination of multiport memory andnetwork technology as discussed above.

[0134] Route frame to fabric process 608 reads the destination portidentifier associated with data received from any process 606, 618, 620,624, or 628 and passes the data to manage output queues process 610 witha designation of one or more output queues. From the perspective offabric 213, output queues of a first routing processor's ingress buffer,may serve as source buffers to be transferred to another routingprocessor's egress buffer serving as a destination buffer, as discussedabove. Route frame to fabric process 608 may read data so as toimplement service priorities among processes 606, 618, 620, 624, and628. The priority of data read may be determined by route frame tofabric process 608 in accordance with an identifier of the requestingmember, resource, or port (e.g., a source identification), an identifierof a participating member, resource, or port (e.g., a destinationidentification), which process 606, 618, 620, 624, or 628 provided thedata, statistics from statistics store 601 related to a characteristicof the data or related to a process 606, 618, 620, 624, or 628 in aperiod of time (fixed, specified, or determined as discussed above), apriority associated with the data by the process 606, 618, 620, 624, or628, or a policy value associated with the data by process 606, 618,620, 624, or 628. Route frame to fabric process 608 may format the dataas the payload of a frame according to framing conventions used forfabric 213 and/or framing conventions used for network 101.

[0135] According to various aspects of the present invention, datareceived for routing by process 608 includes policy values from which asuitable output queue may be determined by route frame to fabric process608.

[0136] Manage output queues process 610 receives frames from route frameto fabric process 608 and transfers each frame to fabric 213. Manageoutput queues process 610 may maintain a plurality of output queues,each output queue corresponding to a physical port of router 102 (e.g.,a port connected to a member that issues frames into router 102 forrouting). Manage output queues process 610 may arbitrate among queues toefficiently access fabric 213, or to implement a policy associated witha particular queue or a policy associated with a particular frame. Forexample, when fabric 213 includes a network as discussed above, manageoutput queues process 610 may add fabric network framing to hide network101 framing in the payload of a fabric network frame.

[0137] Preferably, frames having different associated policy values(e.g., different traffic class or different class of service) areenqueued into separate queues, subject to queue servicing rulesimplemented by manage output frames process 610. Further, frames may beenqueued according to source identification, destination identification,and policy values (e.g., one queue for every combination of physicalinput port identifier, traffic class value, and physical output portidentifier).

[0138] Manage egress queues process 612 receives (or recalls) framesfrom fabric 213 and transfers each frame to one or more egress buffers612, each egress buffer may correspond to a physical output port ofrouter 102 (e.g., a port connected to a member that consumes frames fromrouter 102 after routing). Manage egress queues process 612 may maintaina plurality of egress queues to effect arbitrated access to one or moreegress buffers and/or to effect flow control back toward fabric 213.Arbitration and/or flow control may implement a policy value associatedwith a particular egress buffer or a policy value associated with aparticular frame. Data from fabric 213 may be reformatted by manageegress queues process 612 to comply with signaling and framing standardsof network 101. For example, when fabric 213 includes a network asdiscussed above, manage egress queues process 612 may strip fabricnetwork framing to expose network 101 framing.

[0139] Egress buffer 614 supplies frames to network 101. Egress buffer614 may include a large number of queues for storing frames that awaittransmission onto network 101. While in storage, a frame in a queue maybe revised, for example, to accomplish support for virtualization. Whena frame carries a payload from a nonvirtual transaction that is to bedelivered to a participant of a virtual transaction, manage egressqueues process 612 may: (a) parse the frame from fabric 213; (b)determine that modification is desirable; (c) recall at least a virtualdestination port identifier from virtual context table 630; and (d)modify the frame's destination port identifier in accordance with thevirtual destination port identifier before transmitting the payload tonetwork 101.

[0140] Ingress buffer 616 receives frames from network 101. Ingressbuffer 616 may include a large number of queues for storing frames thatawait transmission onto fabric 213. While in storage, a frame in a queuemay be revised, for example, to accomplish support for virtualization.

[0141] Flow process 618 reads frames from ingress buffer 616, parses,classifies, and processes each frame as described in Table 5. TABLE 5Frame Contents Description of Processing Link service request Whenparsed results indicate the frame is a link service request, flowprocess 618 passes any or all of the frame to pass link service requestprocess 603. Indications that a frame is a link service request includethe destination address portion of the frame (e.g. an address reservedfor link service requests according to a protocol of network 101), avalue describing a type of frame, and/or a value describing a protocolto which the frame is compliant. Frame for notice to a When parsedresults indicate the frame is of a type to be supplied to a proxy or foraction by proxy, flow process 618 passes any or all of the frame to passto proxy a proxy process 620. Such a frame may be a control frame ordata frame regarding a transaction involving a virtual member orresource. Such a frame may notify the proxy, effect the state of aproxy, or trigger suitable action by the proxy. Indications that theframe is of a type to be supplied to a proxy include the destinationport identifier portion of the frame (e.g. a network address reservedfor a proxy according to a protocol of network 101, or any fields of theframe identified for processing by a proxy, for example, by anassociated flag obtained from routing table 622 accessed in accordancewith a portion of the frame), a value describing a type of frame, and/ora value describing a protocol to which the frame is compliant. Frameunrelated to a When parsed results indicate that the frame is unrelatedto a subflow or subflow or virtual flow a virtual flow, flow process 618passes any or all of the frame to route frame to fabric process 608.Indications that a frame may be unrelated to a subflow or virtual flowinclude an associated flag obtained from routing table 622 accessed inaccordance with a portion of the frame, or simply a value of adestination port identifier field of the frame. Frame related to a Whenparsed results indicate that the frame is related to a subflow, flowsubflow process 618 passes any or all of the frame to subflow process624. Indications that a frame is related to a subflow include anassociated flag obtained from routing table 622 accessed in accordancewith a portion of the frame. Frame related to a When parsed resultsindicate that the frame is related to a virtual flow, virtual flow flowprocess 618 passes any or all of the frame to virtual flow process 628.Indications that a frame is related to a virtual flow include anassociated flag obtained from routing table 622 accessed in accordancewith a portion of the frame, and/or a value of a destination portidentifier field of the frame. None of the above Flow process 618 maydrop the frame by freeing the ingress buffer space allocated to theframe. Flow process 618 may raise a countable statistic or an errorcondition in concert with dropping a frame. Flow process 618 may passany portion of the frame to report status and errors process 602 tofacilitate rectifying the error condition or avoiding future errorconditions.

[0142] Any of the references made to routing information discussed inTable 5 may provide one or more policy values for output queue selectionas discussed above.

[0143] Pass to proxy process 620 may associate the data (correspondingto a frame) received from flow process 618 with an identifier of aparticular proxy for member process 418 and revise the frameaccordingly. An identifier may be selected from a range of network portaddresses not used by router 102 yet reserved to router 102 by aprotocol of network 101 (e.g., well known addresses). The identifier mayfurther include an object reference. Pass to proxy process 620 thenpasses the data and the proxy identifier to route frame to fabricprocess 608. In one implementation, when a requester directs a controlframe or a data frame to a virtual entity, the frame includes adestination port identifier that identifies the proxy that acts for thevirtual entity. To accomplish passing to the proxy, pass to proxyprocess 620 may route such a frame without revision.

[0144] Routing table 622 includes cross reference information receivedfrom map 211 and information determined by flow process 618. Forexample, routing information as discussed above may include a tuple(e.g., an association) of source identifier/destination identifier thatmay be used to obtain routing information for egress (e.g., anidentifier of a queue, a logical router port identifier, or a physicalrouter port identifier). Such a tuple is herein called a flow; and, arow of the routing table is herein called a flow entry. Generally,information regarding one flow may be organized in one row of routingtable 622. Where more than one row is made necessary by the quantity ofinformation or for representing many-to-one relationships, a portion ofa row (e.g., a flow identifier) may be used in a subsequent access ofthe routing table. The subsequent access is herein called a subflow.Subflow entries may be used to describe resources on a subnetwork of amember as discussed above.

[0145] The routing information for egress recalled from routing table622 may correspond to an output queue 610, a fabric network address, anegress queue 612, and/or an egress buffer 614. Particular advantages arerealized by identifying each of the above to the same physical portidentifier so that the destination port identifier is sufficient todirect the frame out of the appropriate physical port of router 102. Thesame tuple may be used to obtain (e.g., simultaneously with the physicalport identifier for egress) one or more policy values used to implementpolicies as discussed above.

[0146] Information determined by flow process 618 may include anidentifier of a resource from a request frame. For example, when arequest frame includes a destination port identifier of a member, atransaction identifier, and a resource identifier (the resource being ona subnetwork of the member) subsequent frames from the requesting memberor from the resource that accomplish data communication may omit theresource identifier relying on the destination member identifier and/orthe transaction identifier for routing. In such a case flow process 618may determine that the frame is a request conforming to a protocol thatmakes such an omission and store in routing table 622, context table626, or virtual context table 630 the resource identifier in associationwith the transaction identifier and/or in association with thedestination port identifier for future reference.

[0147] Subflow process 624 generally receives from flow process 618 dataregarding a frame addressed to a member and a resource on a subnetworkof the member. Subflow process 624 associates the data with a routerport identifier. Subflow process 624 may obtain the router portidentifier and policy values from routing table 622 as a flow lookupdiscussed above. Subflow process 624 may read a subflow (e.g., perform asubflow lookup) from routing table 622 accessed in accordance with aportion of the data and/or information recalled from the flow lookup.Subflow process 624 may further read context table 626 as directed byinformation recalled in the flow lookup and/or the subflow lookup and/orby a portion of the data. Subflow process then applies policiesindicated by policy values that may be associated with the flow and/orthe subflow entries in routing table 622 and/or associated with theresource entry in context table 626. Subflow process 624 then passes thedata, the router port identifier, and policy values, to route frame tofabric process 608.

[0148] When a transaction is begun involving one or more virtual devices(herein called a virtual transaction) routing process 208 identifies aframe that signals the beginning of the virtual transaction, and inresponse to that frame and in accordance with the protocol identified tothe virtual transaction, performs the remainder of the virtualtransaction in concert with beginning and performing a correspondingtransaction with a physical member and/or device (herein called anonvirtual transaction). The protocol used in the nonvirtual transactionmay differ from the protocol used in the virtual transaction. In otherwords, there may be no one-to-one correspondence between frames (e.g.,frames for inquiry, data transfer, reply, status, and error conditions)of the virtual transaction and frames of one or more nonvirtualtransactions that implement the virtual transaction on nonphysicalmembers and/or nonvirtual resources. Policies implemented for thevirtual transaction may differ from policies implemented for thenonvirtual transaction, for example, to assure meeting a policyassociated with the virtual transaction.

[0149] Virtual flow process 628 receives from flow process 618 datacorresponding to a frame of a virtual transaction (e.g., addressed to avirtual member and/or virtual resource). Virtual flow process 628associates the data with a router port identifier and prepares data fora frame of a nonvirtual transaction (e.g., addressed to a nonvirtualmember and/or a nonvirtual resource). Virtual flow process 628 mayobtain the router port identifier and policy values from routing table622 as discussed above as a flow lookup using a tuple of sourceidentifier/virtual destination identifier. Virtual flow process 622 mayread context table 626 as discussed above as a subflow lookup using thesame tuple as for the flow lookup accompanied by a portion of theresults (e.g., flow identifier) of the flow lookup and/or data fromprocess 618.

[0150] A nonvirtual resource may have a state different from the stateof the corresponding virtual resource. The state of a virtual resourcemay be tracked by a proxy as discussed above with reference to proxystate 420. For example, support for a virtual storage resource may allowread/write access in a manner unsuited to efficient operation of aphysical resource (e.g., contiguous sectors in reverse order of cylinderspin) so as to satisfy particular efficiencies realized by a process ofthe requesting member. An implementation of such a virtual storageresource may include caching and buffering as discussed above withreference to cache agent 422. Further, a virtual storage resource may bemapped (e.g., on a sector basis) to any mix of nonvirtual devices andportions of nonvirtual devices. A virtual storage resource may beaccessed as a conventional block device having virtual cylinderscomprising virtual pages, and virtual pages comprising virtual sectors.

[0151] Virtual flow process 628 may use identifiers recalled from theflow lookup, the subflow lookup, and/or the context table 626 todetermine a nonvirtual resource identifier; and then refer to page table632 and sector table 634 to obtain virtual to nonvirtual crossreferences from which a nonvirtual page and sector (e.g., a nonvirtualblock) may be identified. After the nonvirtual destination port andnonvirtual block are determined, virtual flow process may perform alogical flow lookup and possibly a logical subflow lookup to obtain arouter output port identifier, nonvirtual resource identifier, andpolicies to implement. In an alternate implementation, the router outputport identifier, nonvirtual resource identifier, and policy values areobtained directly with the initial flow and subflow lookups without alogical flow or logical subflow lookup.

[0152] Particular advantages are realized by locating logical tophysical and virtual to nonvirtual cross reference information in tablesthat may be accessed by multiple routing processes (e.g., sharedmemory). Port table 636 may be stored in shared memory indexed bylogical port identifier to provide a corresponding physical portidentifier (more than one may be provided for broadcast and multicastapplications). A logical port identifier may correspond to routinginformation provided by an administration process as discussed above(e.g., a group name, zone name, path name, or suitable reserved label).Virtual context table 630 may be stored in shared memory indexed by anidentifier of the virtual member, virtual resource, and/or virtualtransaction to provide a corresponding nonvirtual transactionidentifier. In an alternate virtual flow process implementation, thevirtual flow process obtains the router output port identifier (e.g., alogical to physical lookup) and may also obtain policy values byaccessing either port table 636 or virtual context table 630.

[0153] Virtual flow process 628 identifies data to route frame to fabricprocess 608 for use in one or more frames for one or more nonvirtualtransactions that implement the virtual transaction indicated by framesreceived by flow process 618. Data may include the router output portidentifier, nonvirtual resource identifier, nonvirtual block, nonvirtualtransaction identifier, and policy values.

[0154] A method for routing frames according to various aspects of thepresent invention includes any method that includes one or more of thefollowing: (a) implementing different policies for each of differentresources that may share a common member identifier, (b) implementingone or more nonvirtual transactions to accomplish the intent of avirtual transaction; (c) obtaining nonvirtual block identificationcorresponding to virtual block identification; (d) arbitrating amongqueues on the basis of a grant pool for each of a plurality of servicetypes or traffic classes, and (e) implementing a stall for one ofseveral resources that share a common member identifier or resourceidentifier. For example, a method 700 of FIGS. 7-10 that is performed byany router 102-105 as described above and may be performed by anyrouting process 208 proceeds as follows.

[0155] To process a flow, a frame is received comprising indicia of adesired flow (702). The desired flow may be indicated by any combinationof a source identifier, a destination identifier, and a protocol.Indicia of the flow are used as an index (704) to obtain flags, policyvalues, and an output queue identifier, all from one or more tables(e.g., each table may be a data structure, a record of a database, or aset of data structures or records of a database). The flags are thenused (706) to determine which of five processing scenarios should applyto the subject frame.

[0156] Use as an index includes use in an exact match search and use ina maximal match search. Searching may be facilitated by contentaddressable memory circuitry that receives the index (e.g., a tag havingdata and ternary designations: must match, must not match, don't care)and provides flags indicating the extent of the match. When more thanone match is found, use of the maximal match is preferred. A match maybe better (more maximal) than another match when more fields of the tagmatch, when higher priority fields of the tag match, or a weightedcombination of component fields matches. When tag fields are arranged bypriority (or weight), a longest match (e.g., greatest number ofcontiguous fields or bits) may provide a maximal match. A field valuemay indicate a wild card accepting any result as a match.

[0157] A transaction may include several frames to be routed. In thefollowing discussion, routing frames of a transaction is accomplished byrouting all frames of a transaction primarily for control as controlframes and all frames of a transaction primarily for data transfer asdata frames.

[0158] If the flags indicate the frame is a link service request, theframe is passed (708) to a supervising process that accomplishes theintent of the link service request as discussed above. As a consequenceof processing the link service request, data may be provided by thesupervising process for a frame to be placed (720) in the output queueidentified previously (704).

[0159] If the flags indicate a type-A nonvirtual frame, one or morepolicies are applied (718) to effect a quality of service and the frameis placed (720) in the output queue identified previously (704).

[0160] If the flags indicate a type-B subnetwork transaction, a resourceidentifier and policy values associated with the resource identifier areobtained (712) first by parsing the frame according to the protocol todetermined the resource identifier of the subnetwork of the destinationand second by using the resource identifier in a subflow lookup to getpolicy values that have been associated to the destination portidentifier and the resource identifier. Then one or more policies areapplied (718) to effect a quality of service, and the frame is placed(720) in the output queue identified previously (704).

[0161] If the flags indicate a type-C virtual data frame, theidentifiers determined by prior parsing (702) are taken as virtualsource identifier and virtual destination identifier. Data for anonvirtual transaction frame is obtained (714) by further parsing thereceived frame (702) according to the protocol to determine a virtualresource identifier and virtual block description. The virtual resourceidentifier is translated by reference to one or more cross-referencetables (e.g., tables of the form discussed above at 704) to a nonvirtualresource identifier. The virtual block description is translated byreference to one or more cross-reference tables (e.g., tables of theform discussed above at 704) to a nonvirtual block description.Processing as discussed for type-B frames may be accomplished for thenonvirtual destination port identifier and the nonvirtual resourceidentifier; or, policies identified with the nonvirtual destinationidentifier and nonvirtual resource identifier are applied (718) and aframe comprising the nonvirtual resource identifier and the nonvirtualblock description is placed (720) in the output queue identified to thenonvirtual destination port identifier (704).

[0162] If the flags indicate a type-D virtual control frame, the frameis identified (716) to be routed to a suitable proxy, the frame isplaced (720) in the output queue associated with a managing process 204or proxy process 418 (704).

[0163] After a suitable frame has been placed in an output queue,processing continues with the next frame (702).

[0164] To implement a policy according to various aspects of the presentinvention, data particular to a transaction is maintained up to date.Such data may include the state of a resource, proxy state, and/orcross-reference information for determining a nonvirtual transaction forimplementing a virtual transaction. For example, when administratingprocess 202 defines a new or revised virtual member or virtual resource,managing process 204 may launch a new proxy process 418, and managingprocess 204 in cooperation with supervising process 206 may update map211 for use by all routing processes 208. Proxy state is consequentlyupdated. When a transaction is completed normally or terminatedabnormally, data particular to the transaction (e.g., a saved resourceidentifier, or statistics) may be discarded and processing resourcesthat may have been allocated are freed. Routing process 208 maintainstransaction data (802) by cooperating with a supervising process forshared access to map 211.

[0165] Queue controls (804) and arbiter controls (806) are set inaccordance with policy values. Queue controls may designate prioritiesamong competing queues, flow control Strategies and thresholds for eachqueue (e.g., actions to take when a queue is getting full or gettingempty), and/or effect a stall on a queue preventing further input (e.g.,allowing an input queue to empty) or preventing further output (e.g.,allowing an output queue to fill). Arbiter controls may designate flowcontrol strategies and thresholds for each of a group of queues of thesame priority (e.g., same traffic class). Queue controls and arbitercontrols may be set by register transfer instructions when queue controland arbitration are effected by logic circuits. Application of a policymay include accumulating (808) statistics related to frames routedand/or queue and arbiter operations for use by a managing oradministrating process as discussed above.

[0166] According to various aspects of the present invention, multiplecopies of information from a frame are avoided to avoid the time memoryspace consumed by making a copy. The one copy of frame data may persistin an ingress buffer until all reference to it has been accomplished(e.g., a corresponding frame is transferred to the fabric or the frameis dropped). In the discussion above regarding passing a frame or dataof a frame among processes, the data that is passed may be merely apointer to the ingress buffer where frame data can be read indirectly(via the pointer), a handle to context where pointers and simple valuesare stored, or a pointer to a row of a table where a translation may beobtained.

[0167] Placing a frame in an output queue may be accomplished in amanner that implements a policy. The result of such placement in anon-blocking router is that the frame is eventually transmitted out ofthe router in accordance with a priority. The entry in the queue may bea reference to frame data in an ingress buffer as discussed above, or ahandle to a context having pointers and simple values as discussedabove. Each queue may be a linked list of ingress buffer contents.

[0168] Placing an item into such a queue (enqueueing) may includeinserting an item into a linked list (e.g., storing revised values ofpointers). A policy may affect any of several steps in routing a frame.Routing may include, for example, enqueueing a frame for transmissiononto fabric 213 by making reference in a suitable first queue to theframe as it is stored in ingress buffer 616; servicing the first queueby a first arbiter for transmitting the frame onto fabric 213; receivingthe frame (e.g., essentially the payload) from fabric 213 into egressbuffer 614; enqueueing the received frame by making reference in asuitable second queue to the frame as it is stored in egress buffer 614;and servicing the second queue by a second arbiter for transmitting theframe to network 101. The first and the second arbiters may use the sameor different arbitration techniques.

[0169] The amount of space available for frames in a buffer used for aqueue may be managed by several protocols of fabric 213 and network 101(e.g., backpressure logic or techniques of the type used in FibreChannel) wherein requests for buffer space are sent to a receiving portand granted with the result that an integral number of creditscorresponding to reserved buffer space are received by the requestingport. Buffer contents may be later transferred to another buffer orregion of memory where available space must be requested in advance in asimilar manner (e.g., a buffer dedicated to a particular resource at theend of the segment, or a number of buffers (e.g., end-to-end) alongmultiple segments (e.g., hops) of a communication path through network101. As used herein, a grant or grant pool refers to a buffer spaceallocation mechanism at any level of communication protocol (e.g., acredit or allowance in addition to a credit). Grants may be associatedwith a resource, a segment, a port, an ingress or egress buffer, or afabric channel.

[0170] Any conventional arbitration may be used for arbiters asdiscussed above. Particular advantages are realized according to variousaspects of the present invention by implementing queues with timers.Each timer may facilitate minimal fractional bandwidth for one or morequeues. During a period of time when no timer is lapsed, arbitration mayproceed in a round robin manner or in a manner as discussed below withreference to FIGS. 9 and 10. For simplicity, FIGS. 9 and 10 describearbitration for queues in an ingress buffer. Alternate implementationsof router 102 provide such arbitration for queues in the egress buffer.A non-blocking router may omit operations (e.g., 908, 914, 1006, 1014)related to stalling a queue in either or both of the ingress and egressbuffers.

[0171] When grants for an output queue are received (902), the quantityof grants may be added (904) to a grant pool associated with the queue.The total quantity of grants (corresponding to a total quantity of spacefor frames at the receiving end) may be determined (906) as a so calledgrant pool depth. If the queue is associated with a flow that has beenstalled, the frame may be left (910) in the queue (e.g., in the ingressbuffer) and processing continues with another frame (922, 702). If theflow is not stalled, it is determined whether there are sufficientgrants for transmitting a frame from the queue. If not, the flow isstalled (914) by setting a flag (e.g., the flag that is tested at 908).Otherwise, the frame is transferred (916) to the fabric 213 and removedfrom the queue; the grant pool is decremented (918); a transferredquantity counter (TQC) is adjusted (920) and processing continues withanother frame (922, 702).

[0172] A method for arbitrating among output queues of the samepriority, according to various aspects of the present invention,includes any method that enables all other queues of a group of queuesto empty as much as previously emptied from a queue of the group. Forexample, method 920 of FIG. 10, on removal of a frame from a first queue(e.g., a queue associated with a source port) of a group of queues,includes adding the size of the transferred frame to the TQC associatedwith the corresponding source. If the TQC for this source has a valuenot greater than zero (1004), no further action is taken (1018, 922) andprocessing continues with the next frame (702). Otherwise, the subflowfor this source is stalled (1006) by setting a flag; the positive extentof the TQC (the difference between the TQC value and zero) is assigned(1008) to a variable called the overrun; and the TQC is set (1010) tozero. For each other queue in the group of queues (1012) (assuming allqueues in the group have the same priority for transferring frames tothe fabric), the queue status is reset (1014) from stalled (if it wasstalled) to not-stalled; and the overrun is subtracted (1016) from theTQC for that queue. When all queues of the group have been considered(loop 1012), processing continues (1018, 922) with the next frame (702).

[0173] In an embodiment of system 100 having particular synergies forapplication service providers, storage service providers, and storagearea management, network 101 supports protocols of the type known asSCSI protocols over Fibre Channel protocols. Embodiments of this typeare implemented in accordance with the SCSI-3 family of standards andcompatible specifications described, inter alia, inhttp://www.tl0.org/scsi-3.htm and available through NCITS Online Storemanaged by Techstreet 1327 Jones Drive Ann Arbor, Mich. 48105(http://www.techstreet.com/ncits.html), particularly those standardsidentified as “Information technology—SCSI-2 Common access methodtransport and SCSI interface module” (CAM), “Information technology—SCSIArchitecture Model-2” (SAM-2), (SBC), “Information Technology—SCSI BlockCommands-2” (SBC-2), “Information Technology—SCSI Reduced blockcommands” (RBC), “Information Technology—SCSI-3 Stream commands” (SSC),“Information Technology—SCSI Stream commands-2” (SSC-2), “InformationTechnology—SCSI-3 Medium changer commands” (SMC), “InformationTechnology—SCSI-3 Medium changer commands-2” (SMC-2), “InformationTechnology—SCSI-3 Multi-media commands” (MMC), “InformationTechnology—SCSI-3 Multi-media commands-2” (MMC-2), “InformationTechnology—SCSI-3 Multi-media commands-3” (MMC-3), “InformationTechnology—SCSI-3 Reduced Multi-media commands” (RMC), “InformationTechnology—SCSI-3 Controller commands” (SCC), “InformationTechnology—SCSI Controller commands-2” (SCC-2), “InformationTechnology—SCSI-3 Enclosure commands” (SES), “InformationTechnology—Object-Based storage devices” (OSD), “Informationtechnology—SCSI Primary Commands-3” (SPC-3), “FIBRE CHANNEL SwitchFabric-2” (FC-SW-2), “Fibre Channel” (FC), “Fibre Channel Protocol”(FCP), “Information Technology—Fibre Channel Protocol for SCSI, SecondVersion” (FCP-2), and “FIBRE CHANNEL Framing and Signaling” (FC-FS). Inother embodiments, SCSI protocols over protocols other than FibreChannel protocols may be used with ports as discussed above. In otherwords, a router may support virtual SCSI transactions, for example, overa port that supports a protocol such as SCSI Parallel Interface, SerialBus Protocol, IEEE 1384 (Fire wire), SSA SCSI-3 Protocol, ScheduledTransfer, and Virtual Interface all of which are the subject of currentpublic standards and draft standards.

[0174] According to the terminology defined in protocols for SCSI overFibre Channel, communication is organized to permit an applicationclient to invoke tasks to be performed by a device server. Thecommunication model generally includes a request from the applicationclient to the device server and a response from the device server backto the application client. A request may be either for device service orfor link service. Each task may be part of a task list maintained by thedevice server. A task may be invoked, specified, and controlled by aseries of commands (e.g., linked commands) communicated by theapplication client to the device server. According to this model, amember may have multiple application clients and each application clientmay have multiple initiators. Communication from the application clientis generally directed to a target that may have multiple device serversand each device server may act as a responder.

[0175] As discussed above, communication comprises transactionscomprising frames. As defined under SCSI protocols, the communication(e.g., including commands, data, status, and acknowledgements) comprisesSCSI I/O operations. As defined under Fibre Channel protocol (FCP), eachSCSI I/O operation is accomplished by a Fibre Channel exchange. Whereasan I/O operation includes a request and a response, an exchange includesa series of sequences, and each sequence typically comprises severalinformation units. Each information unit corresponds to a frame asdiscussed above. Each sequence of an exchange is transmitted from anoriginator to a responder. If the roles of originator and responder areto be reversed, the originator sends an indication called sequenceinitiative to the responder and the next information unit is expectedfrom the former responder (now an originator).

[0176] When a member port is recognized by another port to which themember is connected, either the port or the member may initiate a loginprocess. Port login is accomplished with FCP IUs with the result that anidentifier for the port of the member is established and associated withthe port of the fabric (e.g., for system 100, port 160 of member 110 isidentified and associated with port 130 of router 102). Port login mayalso result in a quality of service policy being established for thelink between the member and the port (e.g., link 150) and may define ofaffect policies for all paths that include that link. Functions of FCPthat may be included in such a quality of service policy include classof service, intermix mode, stacked connect requests, sequentialdelivery, dedicated service (e.g., connection-oriented), simplex,duplex, camp on, buffered service, priority, preference, initialresponder process associator; capabilities for acknowledgement, datacompression, data encryption, clock synchronization; X_ID interlock,error policy support, categories per sequence, open sequences perexchange, and end-to-end credits (or grants as discussed below).

[0177] The correspondence of a typical series of SCSI I/O operations toFCP IUs is described in the aforementioned specifications and ispartially summarized in Table 6. The target (e.g., a resource asdiscussed above) may be a block oriented data storage device or aprocess. Generally, a target may include many logical units, eachlogical unit having a logical unit number (LUN). Storage is addressableby a logical block address for a read exchange or a write exchange. Atask is an object (e.g., a process) in a logical unit that accomplisheswork specified by the command or by a sequence of commands. TABLE 6 SCSII/O Operation Primitive FCP Exchange Primitive Command request. AUnsolicited command information unit (IU) (e.g., Fibre Channel commandis specified by a Protocol Command: FCP_CMND). An FCP_CMND IU commanddescriptor block includes a CDB and may include a command referencenumber (CDB) in an initial frame of a (CRN) to assure sequentialperformance of commands by a task. request. Data delivery request. Datadescriptor IU (e.g., FCP Transfer Ready: FCP_XFER_RDY). Used in a writeexchange to inform the initiator that the responder is ready with abuffer to receive a particular block from the initiator. Data deliveryaction. Solicited data IU (e.g., FCP_DATA). Used to transfer data in aread or write exchange with a storage device. For data exchange with aprocess, the send and receive commands are defined analogously. SendCommand Complete. Command status IU (e.g., FCP response: FCP_RSP). Usedto indicate that a SCSI command has been completed. Request orAcknowledge Confirmation IU (e.g., FCP_CONF). command completion.

[0178] SCSI commands include, inter alia, inquiry, report LUNs, blockcommands (e.g., read, write, send, and receive) and extended copy. Aninquiry command provides the initiator with parameters of the target ora component logical unit of the target, such as device type forcompatibility to receive various SCSI commands. Parameters may includeend-to-end credits (or grants) allocated by the target to the initiatorfor a particular logical unit, process, and/or task. A request to reportLUNs provides the initiator with a list of logical unit numbers of aspecified target. An extended copy command directs data from one set oflogical units to be copied to another set of logical units (or to thesame set of logical units).

[0179] SCSI is considered an upper level protocol (ULP) and FibreChannel a lower level protocol (LLP). The lower level protocols include:the physical interface including media, transmitters, receivers, andtheir interfaces (FC-0); the transmission protocols including serialencoding and error control (FC-1); the transport protocols includingframe format, sequence definitions, transfer of data blocks, and classesof service (FC-2); and services concerning several ports at a node(e.g., operations on a hunt group) (FC-3). The upper level protocols(FC-4) generally include application protocols such as SCSI.

[0180] An information unit is transported as a frame. A frame is definedas an FC-2 construct that includes signals recognized as: a start offrame (SOF), a payload, and an end of frame (EOF). For an informationunit, the payload is further defined to include an FC-2 header, an FC-2payload, and a cyclic redundancy check (CRC). Further, for aninformation unit, the FC-2 payload includes one or more optionalheaders, an FC-4 header and an FC-4 payload. The information conveyed bythe various portions of an information unit is described in Tables 7 and8, below. Each frame is formed so that the beginning and extent of eachof these portions is determinable under the conventions of theprotocols. Generally, parsing refers to determining the beginning,extent, and meaning of portions of a frame; and formatting generallyrefers to arranging data for transmission as a frame by placing data inthe order defined by the protocols.

[0181] A flow, as discussed above may correspond to an exchangeidentifier (X_ID) comprising an S_ID and a D_ID. A fully qualifiedexchange identifier (FQXID) further includes an initiator identifier, atarget identifier, an OX_ID, and an RX_ID. The FQXID (as defined in theFibre Channel specifications) is not a complete I_T_L nexus (as definedin the SCSI specifications) comprising an initiator identifier, a targetidentifier, and a logical unit identifier; or, an I_T_L_Q nexus,comprising an initiator identifier, a target identifier, a logical unitidentifier, and a task identifier or tag. A subflow, as discussed abovemay correspond to an I_T_L nexus or an I_T_L_Q nexus. TABLE 7 FC-2 FC-4SCSI Delimiter Start of SOF frame Payload FCP R_CTL Header F_CTL CS_CTLPRIORITY DF_CTL TYPE OX_ID RX_ID SEQ_ID SEQ_CNT S_ID D_ID RO FCP NetworkPayload header Association header Device header FC-4 header LUN CRN Taskattributes Task management R-W-Add CDB OP_CODE LBA XFER_L PARAM_LIST_LALLOC_L CONTROL FCP_DL Data Error CRC Control Code Delimiter End of EOFframe

[0182] TABLE 8 Field Description SOF Any of several ordered sets thatindicate the beginning of a frame. Each start of frame may identify atype of frame to facilitate parsing (e.g., first frame of a sequence,other than the first frame of a sequence, class of service, or type ofsequence that follows based on class of service). R_CTL Routingcontrols. Includes information category describing the information unitas solicited or unsolicited as control, data, command, data- descriptor,or command-status. May identify the frame in cooperation with TYPE aslink control (e.g., ACK), extended link services, or a data frame.Information category may identify frames as FCP_CMND, FCP_XFER_RDY,FCP_DATA, FCP_RSP, and FCP_CONF. F_CTL Fabric controls. May specify thatthe frame is from an initiator vs. a recipient; from an originator vs. aresponder; whether the frame is part of a sequence that is the first,last, or neither the first nor the last sequence of the exchange; andwhether the frame is the last vs. not the last frame of a sequence.Fabric controls may further specify if a transfer of sequence initiativeis to take place. Fabric controls may include a flag that specifieswhether to include PRIORITY in place of CS_CTL. CS_CTL Class specificcontrols. For example, Class 1 is for a connection-oriented servicebetween initiator and target; Class 2 is for a connectionlessmultiplexed service with acknowledgement; Class 3 is for aconnectionless multiplexed service without acknowledgement (e.g. withpossible preference indication); Class 4 is for a virtual circuit thatprovides fractional bandwidth between communicating ports, in-orderdelivery, and acknowledgment; and Class 6 is for multiple simultaneousconnection- oriented services between the same two ports. Class 1controls may indicate simplex or duplex. Class 1 and class 6 controlsmay indicate stacked connect request, camp on, and/or bufferedfunctions. Class 2 and class 3 controls may indicate priority delivery(e.g., a 1-bit value for preference on/off). Class 4 controls mayspecify a virtual circuit identifier VC_ID. A QoSF associates S_ID,D_ID, and VC_ID to identify all frames to which the guaranteed bandwidth(and latency) apply. PRIORITY An integer value (e.g., seven bits)indicating to a router having more than one queue and a serving processthat must choose from several queues (e.g., input port queues,processing queues, output port queues) which of several queues toservice next. The PRIORITY value may include a PREEMPTION bit forrudimentary high/normal or normal/low priority determinations. DF_CTLData frame controls. May specify whether or not the FCP payload includesoptional headers. TYPE Data structure type. May indicate communicationprotocol, for example, SCSI, SNMP, IP, internal FC-SW, or VI. Mayindicate IU types for that protocol. For example, for a SCSI command,TYPE in cooperation with R_CTL indicates the frame is formatted toconvey any SCSI command (e.g., FCP_CMND having a CDB), to convey data,or to convey an extended link service request (e.g., FLOGI, PLOGI, orRTIN). OX_ID Originator's exchange identifier. May be assigned by anFC-4 process (e.g., a ULP). RX_ID Responder's exchange identifier. Maybe assigned by an FC-4 process (e.g., a ULP). SEQ_ID Sequenceidentifier. May be assigned by an FC-4 process (e.g., a ULP). SEQ_CNTSequence count indicates a serial number of the frames having the sameSEQ_ID. Useful for maintaining frames in-order. S_ID Source identifier.Identifies the network port that transmitted the frame. Typically a24-bit number that identifies the initiator. It may be divided intothree 8-bit portions designating domain (an identifier of a router,e.g., router 102), area (an identifier of a physical output port of therouter, e.g., 130), and loop address (an identifier of a resource on aloop serviced by the port). D_ID Destination identifier. Identifies thenetwork port intended to eventually receive the frame. Typically a24-bit number that identifies the target. It may be divided into three8-bit portions designating domain, area, and loop address. The D_ID mayspecify a group address or a well known address. Well known addressesare reserved values for, inter alia, a multicast server, a clocksynchronization server, a security key distribution server, a timeserver, a directory server, a broadcast alias, an alia server, amanagement server, a quality of service facilitator (QoSF), a fabriccontroller (e.g., managing process 204), or a fabric port. RO Relativeoffset. A displacement in bytes describing the first byte of a payloadrelative to a data buffer that was read to form the payload or a databuffer that will be written when the payload is delivered to itsdestination. The relative offset may be designated as random orcontinuously increasing for different information categories. Networkheader Includes, respectively for S_ID and for D_ID of the FCP header, adesignation of an authority that assigned a name (e.g., CCITT, IEEE) anda name identifier (e.g., 60-bit value, WWPN). Association headerIncludes, respectively for S_ID and for D_ID of the FCP header, aprocess identifier (e.g., a 56-bit object reference used with CORBA).Device header Provides to a ULP additional identification of theexchange already identified by the FCP header. LUN Logical unit number.Identifies a resource of the member at the destination network port. Maybe a WWPN or a suitable 64-bit identifier. CRN Command reference number.May be used to assure that SCSI commands are performed in-order. Taskattributes May specify which task queue, type of task queue, and theposition in that task queue at which the task defined by this exchangeis to be inserted. For example, simple queue, head of queue, orderedqueue, ACA queue, and untagged task. Task management Specifiesoperations on a logical unit and/or a task queue associated with alogical unit, such as: abort task set, clear task set, reset a logicalunit, reset a target, and clear an ACA. R-W-Add May indicate by a singlebit (facilitating parsing) whether the CDB is for a read command or awrite command or neither (and analogously a send or receive commandreferring to a target process). May also specify an additional lengthfor an extended length CDB. An extended length CDB may convey a virtualLUN through a fabric. CDB Command descriptor block. OP_CODE Operationcode. Specifies the SCSI command (e.g., PLOGI, REPORT LUNS, READ, WRITE,SEND, RECEIVE) LBA Logical block address. May include page number (e.g.,11 bits), sector number (e.g., 11 bits), and block offset (e.g., 11bits) designating a 512- byte block that is a portion of a sector.XFER_L Transfer length. PARAM_LIST_L Parameter list length. ALLOC_LAllocation length. CONTROL May specify whether the command is part of aset of linked commands. May also indicate controls for a cachemaintained by the device server, for example, specifying to disable pageoutput from the cache (DPO), and force unit access (FUA) to supercedecache access. CRC Any code, typically a cyclic redundancy check code,that may be used by the receiver to verify the integrity of all or aportion of the transmitted payload. EOF Any of several ordered sets thatindicate the end of a frame. Each end of frame may identify a type offrame to facilitate parsing or link control functions (e.g., terminationof a class 4 circuit, content of the frame is invalid, last frame of asequence, or other than the last frame of a sequence).

[0183] Table 9 briefly describes some of the contents of FCP IUs thataccomplish a SCSI write command. The IUs in Table 9 form one exchange.Each IU is a sequence of that exchange. For each IU, the S_ID identifiesthe transmitting port (the originator, generally having sequenceinitiative) and the D_ID identifies the receiving port. These alternate,though the identity of the initiator and the target are unchangedthroughout the exchange. Note that the LUN is conveyed in the FCP_CMNDCDB and is not included in the FCP_XFER_RDY, FCP_DATA, or FCP_RSP IUs.To implement a quality of service at the logical unit level, the logicalunit number corresponding to the exchange must be recorded from theFCP_CMND IU; and, referred to for other IUs of the exchange. TABLE 9Information Unit Brief Description of Selected Particular ContentsFCP_CMND SOFi2 (Class 2); OX_ID; S_ID is originator of this exchange;S_ID is initiator of this FCP_CMND sequence; This is the first frame ofthe sequence; End sequence (i.e., this frame is the end of the FCP_CMNDsequence); Transfer sequence initiative to responder; EOFn (normal); ACKSOFi2; RX_ID; EOFt (terminate); FCP_XFER_RDY SOFi2; FQXID; S_ID isresponder in this exchange; S_ID is initiator of this FCP_XFER_RDYsequence; End sequence; Transfer sequence initiative to initiator; ROfrom LBA to be written; EOFn; ACK SOFi2; EOFt; FCP_DATA (one of SOFi2;FQXID; Originator; Initiator; End sequence; Transfer sequence several,each initiative; data to be written at RO from LBA; EOFn; followed by anACK) ACK SOFi2; EOFt; FCP_RSP SOFi2; FQXID; Responder; Initiator; Lastsequence of this exchange; End sequence; Transfer sequence initiative;EOFn; ACK SOFi2; EOFt;

[0184] The terminology used to describe system 100 may differ somewhatfrom the terminology defined in the FCP specifications. In the FCPspecifications, a fabric is an entity having ports that routes framesbetween its ports using only the D_ID from the FC-2 header. A path is aroute through the fabric from a source to a destination. A path mayinclude one or more hops. A fabric may include multiple switches, eachswitch being an entity defined as a fabric element having ports, a pathselector, an address manager, a fabric controller, a router, and aswitch construct that transports frames between ports as directed by therouter. A router, as defined in the FCP specifications, is an entitywithin a switch that determines for each received frame what port todirect the received frame so as to accomplish a connectionless delivery.System 100 is described herein in broad terminology as an example of animplementation according to various aspects of the present invention. Toprepare an FCP SCSI implementation according to various aspects of thepresent invention, the specific functions of the FCP and SCSI protocolspecifications are generally mapped as an instance of the functions andstructures described herein that may bear the same or differentnomenclature. Access controls discussed with reference to system 100 areenforced by a router or a proxy, whereas access controls under SCSI andFCP protocols may be enforced by the target (e.g., a device server).

[0185] As discussed above, routing information as determined by anadministrating process or a managing process may include an I_T_L nexus(or I_T_L_Q nexus) for a virtual or nonvirtual member or resource. Forexample, a managing process may launch a proxy for each I_T_L or I_T_L_Qnexus that refers to a virtual identifier (e.g., a virtual member, or avirtual LUN of a nonvirtual or virtual member).

[0186] A router, according to various aspects of the present invention,includes any switch that implements architecture 200 as discussed above.In one implementation, a router includes a supervising processor and aplurality of routing processors, the routing processors being coupled toa fabric comprising a ring network. In another implementation, thefunctions of routing process 208 are implemented in an integratedcircuit comprising a frame processor, multiple interfaces for ports tonetwork 101, and circuits that implement a serial slice of the ringnetwork of the fabric. For example, router 102 of FIGS. 11-14 includesmanaging processor 1112; local console 1102 coupled to managingprocessor 1112; remote console 1106 coupled via bus 1104 to managingprocessor 1112; host bus adapter 1140 coupled 1142 between managingprocessor 1112 and a frame I/O port 1198; erasable programmable memory(EPM) 1114 coupled to managing processor 1112; random access memory 1116coupled to managing processor 1112; and a plurality of routing circuits1150-1152 coupled to managing processor 1112 via local area network(LAN) bus 1132, EPM bus 1134, and test bus 1136. A ring 1170 connectsthe plurality of routing circuits to provide functions of fabric 213.Each routing circuit 1150-1152 includes supervising processor 1160,memory circuit 1162, and a plurality of port logic circuits 1186-1188.Each port logic circuit provides several frame I/O ports 1192 and 1194(for routing circuit 1150); and frame I/O ports 1196 and 1198 (forrouting circuit 1152). In one implementation, a router 102 having 20frame I/O ports is formed on one printed circuit board (excludingconsoles 1102 and 1106 and network 1104).

[0187] A managing processor includes any stored program computer circuitthat manages operations of one or more supervising processors byaccepting paths from an administrating process, providing reports to anadministrating process, providing routing information to one or moresupervising processes, governing operation of one or more supervisingprocesses to assure policy effectivity on one or more links, serving asa proxy, and operating a cache—all, for example, as discussed above. Forexample, managing processor 1112 may include any computer circuit havinginterfaces to memory and communication buses and cooperating with a hostbus adapter. Managing processor 1112 provides a conventional interfaceto memory for program storage and work space. Program memory, EPM 1114,may include any persistent store (e.g., erasable programmable memory,disk, and RAM) for storage of instructions for processes described withreference to FIG. 4, an operating system, and suitable device drivers.Workspace memory, RAM 1116, may include any memory circuit (e.g., RAM,EPM, cache memory, or disk) for storage of data described with referenceto FIG. 4. Managing processor 1112 supports one or more consoles 1102and 1106 that accept input from an operator. Managing processor 1112communicates with host bus adapter 1140 via line 1144 to send andreceive frames. Managing processor 1112 communicates with supervisingprocessors via a bus (e.g., a local area network) such as LAN 1118,1132, 1152. Managing processor 1112 transfers data for image updatesfrom EPM 1114 to routing circuit memory (e.g., 1162) via EPM bus 1120,1134, 1154. Managing processor 1112 communicates with supervisingprocessors for diagnostic, test, and watch dog purposes via test bus1122, 1136, 1156. In one implementation, LAN 1132 has physical andlogical capabilities of the type known as Ethernet (see IEEE Std.802.3), EPM bus 1134 has the physical and logical capabilities of thetype known as a PCI bus (see PCI Local Bus Specification by PCI InterestGroup, Portland Oreg.), and TEST bus 1136 has the physical and logicalof a conventional asynchronous serial communication interface (e.g.,using ASCII character codes for commands, addresses, status, and data).Managing processor 1112 may control fans, power supplies, EPM and otherdevices using a two wire serial interface of the type known as an I²C(see I²C Bus Communication by Philips Semiconductor).

[0188] In one implementation, managing processor includes an IntelSocket 370 440-BX chip set hosting an open sources operating system, forexample, of the type known as Linux.

[0189] A console provides a GUI for an operator (human or automated) tospecify particular values for router configuration and for displayingstatus, reports, error messages, warnings, and prompts. For example,local console 1102 is coupled in any suitable manner to managingprocessor 1112. At any time one or more remote consoles 1106 may becoupled via network 1104 to managing processor 1112. Local console andremote consoles are functionally similar in displays and controls. Forexample, these consoles may be implemented with any client computer(e.g., a terminal, workstation, or personal computer).

[0190] A host bus adapter provides an interface for frame communications(e.g., as described above with reference to SCSI). For example, host busadapter 1140 includes an interface to connect to a physical port ofrouting circuit 1150 via line 1142. Host bus adapter 1140 may transferframes or portions of frames after parsing and error correction tomanaging processor 1112 or RAM 1116 (e.g., directly via lines notshown). Host bus adapter 1140 may transfer data for frames or portionsof frames (e.g., payloads) from managing processor 1112, EPM 1114, orRAM 1116 and perform frame assembly in any suitable manner (e.g.,determining header and error control data for one or more frames). Datatransfer may utilize direct memory access techniques and/or descriptorsas discussed below. In one implementation, the managing processor andhost bus adapter are provided on a single integrated circuit substratethat provides one or more multi-conductor parallel digital interfacesfor coupling to consoles, memory, and routing circuits.

[0191] A routing circuit includes any circuit that routes framesaccording to identifiers (e.g., addresses) as discussed above. Forexample, router 102 may include one or more routing circuits 1150-1152each coupled to at least one managing processor 1112 for performingsupervising and routing processes as discussed with reference to FIGS. 5and 6.

[0192] Fabric 213 of router 102 (FIG. 2) is implemented by ring 1170shown functionally as one line though any suitable number of bus orpoint-to-point conductors are used in various implementations. In oneimplementation a router 102 has only one routing circuit 1150,simplifying design of ring 1170. Ring output 1172 from one port logiccircuit 1186 is coupled (directly or through other port logic circuits)to ring input 1174 of a subsequent port logic circuit 1188.

[0193] Alternatively, ring 1170 extends between routing circuits so thateach routing circuit 1150 communicates with each other routing circuit1152. A ring output of a port logic circuit 1188 of a routing circuit1150 is coupled to ring input of a subsequent port logic circuit of asubsequent routing circuit 1152. A ring permits frame I/O from anyphysical port of router 102 (e.g., ports 1192, 1194, 1196, and 1198) tobe routed to or from any other physical port of router 102.

[0194] Each routing circuit supports a multiplicity of router ports,generally of identical functionality. Each router port may be coupledfor frame I/O to any one of a member of system 100, another router ofsystem 100 (e.g., an expansion port), a console as discussed above, or ahost bus adapter 1140.

[0195] A supervising processor includes any stored program computercircuit that manages operations of one or more port logic circuits byaccepting maps from a managing process, providing status to a managingprocess, providing and updating routing information to one or morerouting processes, acting on link service requests, providing linkservice replies, advising proxy processes (e.g., of link serviceactions, link state, network traffic, events, or configuration) that mayaffect operations performed by the proxy, managing shared use ofcommunication and memory facilities shared by routing processes, andgoverning operation of one or more routing processes to assure policyeffectivity on one or more links—all, for example, as discussed above.For example, supervising processor 1160 may include any computer circuithaving interfaces to memory and communication buses. Supervisingprocessor 1160 may provide any conventional interface to port logiccircuits and memory. For example supervisory (SUPRV) bus 1176, 1164couples supervising processor 1160 to any number of port logic circuits1186-1188 and to memory circuit 1162. In one implementation, SUPRV bus1164 has physical and logical capabilities of the type known as PCI busas discussed above. Supervising processor 1160, any port logic circuit1186-1188, or memory circuit 1162 may become master of SUPRV bus 1176for directing data transfer operations. By permitting bus masterfunctions from any port logic circuit, efficient use of SUPRV bus 1164results. Such use may assure policy effectivity for a particular port.Port logic circuits 1186, 1188 and memory circuit 1162 may include CSRs(e.g., for DMA control configuration) that are mapped to addresses ofthe PCI bus.

[0196] In one implementation, supervising processor 1160 includes asingle chip computer having an Intel x86 compatible processor, PCI, I²C,flash memory, GPIO, and memory bus interfaces of the type marketed byAMD as model SC520. Supervising processor 1160 may perform a real timeoperating system of the type known as Linux as discussed above.

[0197] Preferably, operating systems in the managing processor andsupervising processor support interprocess communication between severalof these processors. For example, in one implementation, interprocesscommunication is implemented using Common Object Request Broker Agent(CORBA) software of the type that allows processes and subprocesses tobe identified (e.g., by an object reference). An administratingprocessor may obtain the services of any object made available via CORBAhosted on any managing processor or supervising processor. For example,managing process 204 may include objects for access control listmaintenance, policy value maintenance, group membership maintenance,zone membership maintenance; and, supervising process may includeobjects for statistics probes (e.g., permitting control of statisticsgathering as to what to gather and when), and routing table maintenance.Managing and supervising processes may include agents that define APIsfor one or more objects to simplify inter-object communication andcontrol.

[0198] A memory circuit provides multiple access to routing information,status information, and configuration information. For example, memorycircuit 1162 is coupled to supervising processor 1160 via SUPRV bus1177, 1164 (e.g., for obtaining routing information as updates ofimages) and to port logic circuits 1186-1188 via ROUTE bus 1178, 1166(e.g., for responding to demands from port logic circuits for routinginformation, status of other port logic circuits, and configurationinformation). Each port logic circuit may be coupled to memory circuit1162 via an independent channel effected via dedicated lines (e.g.,separate buses) or dedicated time slots on a multiplexed bus.

[0199] A port logic circuit includes any circuit that provides at leasta physical interface to one or more frame I/O ports, cooperates withother port logic circuits 1186-1188 via a fabric, and accesses memoryfor routing information. In one implementation, a port logic circuitprovides a logical interface for each frame I/O port so that asupervising process or a routing process may send and receive data via alogical port using an API in some ways independent of frame structureand signaling protocol of the physical port. In one implementation, eachport supports both Ethernet and Fibre Channel frame structures andsignaling protocols so that the same routing process and the samesupervising processes may communicate with ports regardless of whetherthe port is from time to time physically connected to an Ethernet linkor a Fibre Channel link. For example, a group of frame I/O ports 1192supported by port logic circuit 1186 may include a physical interfacefor each of four links, each link being compatible with Ethernet orFibre Channel.

[0200] A supervising processor in one implementation according tovarious aspects of the present invention includes a first bus for aprocessor, memory, and interfaces; a second bus; and a bridge betweenthe first bus and a second bus. The processor may have exclusive controlof the first bus to simplify program operations performed by processeshosted by the processor. The processor may cooperate with otherprocessors intermittently controlling and relinquishing control of thesecond bus to facilitate maximum efficient use of the capacity of thesecond bus. For example, supervising processor 1160 includes bus 1204(e.g., a suitable multi-conductor parallel digital bus) coupled toprocessor 1202, program store 1206 data memory 1208, serial controller1210, persistent store 1212, I/O bus controller 1214 coupled between bus1204 and bus 1216 (e.g., a PCI bus) to perform functions of a bridge;and LAN controller 1218 coupled to bus 1216. Supervising processor 1160is coupled to TEST bus 1136 via line 1156, EPM bus 1134 via line 1154,LAN bus 1132 (e.g., Ethernet) via line 1152, and SUPRV bus 1164 via line1176. Any conventional circuits may be used to implement the functionsof supervising processor 1160 including any mix of memory: volatile andnonvolatile (e.g., erasable programmable memory). Nonvolatile memory maybe used to store programs (e.g., EPM of store 1206) and/or configurationvalues (e.g., persistent store 1212). Configuration values may includeany suitable values that facilitate the assembly of routing circuit 1150in commercially desirable configurations utilizing similar components(e.g., populating a printed circuit assembly to various extents for avariety of router models). For example, configuration values may includethe number of port logic circuits, the electrical position of adistributing circuit in the fabric ring, the addresses (via SUPRV bus1164) of installed port logic circuits, addresses that describeallocations of memory 1162 to port logic circuits (e.g., forconfiguration of port logic circuits and communication betweensupervising processor 1160 and particular port logic circuits), anddefault port characteristics (e.g., physical interface capabilities orphysical port identifiers).

[0201] A memory circuit in one implementation according to variousaspects of the present invention provides routing information (e.g.,including cross reference information) by the cooperation of sharedrandom access memory, content addressable memory, and random accessmemory that is addressed at least in part by data recalled from contentaddressable memory. For example, memory circuit 1162 includes memorycontroller 1302, multi-purpose memory 1304 coupled via line 1303 tomemory controller 1302, content addressable memory (CAM) 1306 coupledvia lines 1305 and 1307 to memory controller 1302 and coupled via line1309 to random access memory (RAM) 1312. Random access memory 1312 isalso coupled to memory controller 1302 via line 1313.

[0202] Memory controller 1302 is coupled to SUPRV bus 1164 via line 1177and coupled to ROUTE bus 1166 via line 1178. Generally, configurationvalues received via SUPRV bus 1177 are stored in multi-purpose memory1304 via line 1303. Routing information (e.g., maps, image data, andupdates) received via SUPRV bus 1177 is stored in CAM 1306 and RAM 1312.When a request for routing information is received via ROUTE bus 1178 bymemory controller 1302, memory controller 1302 presents a query (e.g., atag) via line 1305 to CAM 1306. Tags presented to the CAM may have oneof 8 types as indicated by a 3-bit field. Typical queries are describedin Table 10. TABLE 10 Purpose of Query Query Components Flow lookup tagtype; source identifier (e.g., value from S_ID field of received frame);destination identifier (e.g., value from D_ID field of receivedframe—may be virtual); class of service (e.g., indicated by SOF analyzedby 1406, value of CS_CTL field of received frame); protocol identifier(e.g., as determined by parser 1408 mask/pattern comparisons); inputphysical port identifier (determined by 1406); input physical port type(e.g., port speed, signaling protocol; determined by 1406);configuration settings (e.g., CSR values set by processor 1424); Subflowtag type; all fields of a flow lookup; flow identifier (from flow lookupCAM lookup associated data); Virtual flow tag type; all fields of a flowlookup and a subflow lookup; virtual member lookup identifier (e.g., adestination port identifier such as a D_ID field value from the receivedframe formatted to be recognized as a virtual port identifier); avirtual resource identifier (e.g., a LUN field value from the receivedframe recognized as virtual by association with the virtual memberidentifier);

[0203] CAM 1306 responds to a query by providing a flag on line 1307indicating a successful search. When the search is successful, data online 1309 provides an address to RAM 1312. RAM 1312 responds to theaddress by providing additional query results as data on line 1313described in Table 11. When the search is successful, data from RAM 1312(also called CAM associated data) on line 1313 is valid. CAM associateddata is described in Table 11. TABLE 11 Query RAM 1312 Response (line1313) Flow lookup priority (e.g., traffic class); output physical portidentifier; flow identifier (e.g., assigned by routing processor uponreceipt of FCP_CMND from initiator, a hashed version of source anddestination world wide port names created by the parser); flag forsubflow lookup required; output port speed; action code (e.g., 2 bits);flag for stall; flag for default route; marking for output frame (e.g.,revised CS_CTL value); mid-switch stage (e.g., 4-bit hop count);statistics sample interval; statistics index (e.g., identifies whichcounter should be used for countable events associated with this flow);Subflow resource identifier (e.g., for SCSI-3 protocol on FCP, logicalunit number lookup (LUN); for Virtual Interface, VI handle ofparticipating process); flag for routing processor action associatedwith the type of frame as determined by parsing; process identifier forrouting processor (e.g., a jump vector, or object reference); Virtualflow page table start address; page size (allows programmable pagesizes); sector lookup size (allows programmable sector sizes); shiftvalue (used to determine page boundary crossing); flag set to indicateframes to this virtual LUN should be discarded (e.g., LUN not defined,or does not presently exist); flag set to indicate the virtual LUN isbusy (e.g., frame should be stalled or routed to managing processor forrouting by proxy); flag set to indicate routing for the virtual LUN isdisabled (e.g., frame should be routed to managing processor for routingby proxy);

[0204] A method for revising the configuration of a plurality of routingprocessors includes in any order: (a) for each virtual entity and eachrouting processor to be reconfigured (e.g., each processor that usesrouting information implementing routing for a particular virtualentity), setting a flag to indicate that routing for the virtual entityis disabled; (b) routing to a managing processor for dispositionsubsequently received frames (e.g., both control frames and data frames)that indicate the virtual entity as a destination; (c) enabling proxyprocesses performed by the managing processor to respond to or routesuch subsequent frames; (d) storing new routing information for avirtual entity in a memory accessible by a routing processor; and (e)clearing the flag(s) in router(s) previously set so as to enable routingof traffic for the virtual entity in accordance with the new routinginformation. New routing information may be stored in one router (e.g.,for access by one or more routing processors or frame processors) or inseveral routers facilitating routing for one or more virtual entities(e.g., for distributing the processing burden of virtualization,security, or redundancy).

[0205] Memory controller 1302 provides a response on ROUTE bus 1178 toeach query received on ROUTE bus 1178. Information conveyed by such aresponse includes the data described in Table 11 without the address ofRAM 1312. When the query is accompanied by an identification of thequery (e.g., a worklist pointer value, or an identifier of a queue fromwhich the submitter composed the query), the response may be accompaniedwith a suitable corresponding identification of the query.

[0206] In one implementation, CAM 1306 includes a content addressablememory of the type marketed by Lara Networks Inc. as model LNI7020.Memory controller 1302 includes a CAM controller of the type marketed byLara Networks Inc. as model LNI8010.

[0207] Memory controller 1302 may provide address mapping so that aparticular routing process 208 may access a unique portion ofmulti-purpose memory for its particular configuration or communicationneeds; and all instructions for separate routing processes may beinstalled in separate port logic circuits using identical instructionsin each routing process. By providing address mapping, configurationcontrol of routing process instructions is simplified. In other words,multi-purpose memory 1304 includes an area reserved for each routingprocess 208. Each routing process (e.g., a port logic circuit may haveone or more routing processes) may have a reserved area (not necessarilya contiguous range of addresses). Contents of multi-purpose memory 1304are described in Table 12. TABLE 12 Variable Stored in a Reserved Areaof Multi-purpose Memory 1304 Description Shared tables Each table sharedby several routing processors. Tables may include data structures forthe following: context table, virtual context table, port table, pagetable, and sector table. Configuration values Each configuration tablemay be reserved for use by one routing for each routing processor.Values may include initial values for CSRs and software for processoruse by the routing processor. Supervisor queue for Each queue may bereserved for use by one routing processor and a each routing suitablesupervising processor. May include entries for link service processorrequests, link service replies, and frames to be analyzed and/or routedby the supervisor. Reserved tables Tables used by only one routingprocessor. In various implementations any one or more of the context,virtual context, port, page, and sector tables may be segmented toreduce memory utilization or improve access.

[0208] A port logic circuit includes any circuit that performs a routingprocess as described above. Implementation of such a routing circuit mayinclude one or more of a stored program computer circuit, a microcodedstate machine circuit, and a combinatorial logic circuit (e.g., withcounters and/or state variable storage). The stored program computercircuit and/or microcoded state machine circuit may employ EPM tofacilitate implementing routers 102 in various configurations (e.g.,supporting a wide variety of signaling and communication protocols inone router). By performing different portions of the routing process indifferent circuits, a relatively high degree of parallel processing mayresult with concomitant non-blocking frame I/O processing capacity. Inone implementation, a port logic circuit, inter alia, performs flowrouting, performs subflow routing, performs routing of virtual dataframes, parses frames to facilitate routing virtual control frames to aproxy, gathers and reports traffic statistics, assures specified qualityof service by arbitrating among data flows on ingress and/or on egress,facilitates frame routing via a ring, and communicates with asupervising process via a supervisor queue and interrupts—all, forexample, as discussed above. For example, port logic circuit 1186 ofFIG. 14 includes distributing circuit 1402, egress buffer 1414,arbitrating circuit 1405, media interface circuit 1406, parser 1408,ingress buffer 1410, index 1420, submitter 1422, frame processor 1424,access circuits 1404, cross reference circuits 1425, virtual outputqueue controller 1428, dequeue logic 1412, and statistics store 1426.

[0209] A distributing circuit includes any circuit that performs thefunctions described above with reference to a fabric. For example,distributing circuit 1402, implements functions of a networkimplementation of fabric 213, in particular a ring network. Distributingcircuit 1402 receives signal RING-I on line 1170, recognizes framesaddressed to the physical ports supported by port logic circuit 1186,places at least the payload of such frames (received via line 1430) inegress buffer 1414, responds to signal CONTROL on line 1432 to avoidegress buffer overflow, provides signal CONTROL on line 1436 tosynchronize and/or enable sending, receives (via signal DATA 1434) atleast the payload portion of frames to send to other physical ports, andprovides signal RING-O on line 1172 for input to a subsequent port logiccircuit as discussed above.

[0210] Frames conveyed by signals RING-I and RING-O may also include oneor more of timing signals, header information, error detection andcorrection information, signals indicating priority, quality of service,class of service, traffic class and distribution capacity allocation andarbitration controls. Distributing circuit may receive frames fromdequeue logic 1412 fully formatted for the fabric network; or,distribution circuit may perform formatting functions. Distributingcircuit may provide frames to egress buffer 1414 complete with allfabric network formatting; or may remove formatting by parsing the frameand providing only portions of the fabric network frame to egress buffer1414. Distributing circuit includes address comparison logic so as todetermine whether a frame received on line RING-I is within an addressrange (e.g., matches all or a portion of a physical port address) and ifso to provide at least the payload to egress buffer 1414. Distributioncircuit 1402 is nonblocking, sends every frame that it receives fromsignal RING-I except those delivered to egress buffer 1414, and sendsevery frame that it receives from dequeue logic 1412. Frames that aresent are provided once on line RING-O 1172.

[0211] An egress buffer provides storage for frame payloads to bedelivered to a frame I/O port. An egress buffer may include ring buffersformed from linked lists so that frame payloads of varying length may besuitably stored and accessed. An egress buffer may have separate ringbuffers for each of several traffic classes for the same physical outputport. An egress buffer may support several (e.g., four) physical ports(e.g., with parallel control circuitry and shared memory). The payloadinserted into a ring buffer of an egress buffer already includessuitable indicia of the destination port and is therefore suitable fordelivery from the egress buffer without revision. Such indicia of thedestination port may differ from the physical port identifiercorresponding to the frame I/O port 1192 of this hop (e.g., destinationport 166 may be indicated in a frame delivered out of port 133. See FIG.1).

[0212] For example, egress buffer 1414 (comprising combinatorial logic,memory, and a state machine) includes a ring buffer for each of 4traffic classes. All frames received from distributing circuit 1402 thatare within the address range corresponding to frame I/O port 1102 (e.g.,carrying in a header the exact physical port address of a physical portof frame I/O port 1192) are stored in a ring buffer corresponding to thetraffic class indicated in a header of the frame.

[0213] An arbitrating circuit identifies at a suitable time each framepayload to be sent as a frame and determines which of several competingsupplies of frames should be used as a source of supply for the nextopportunity to send a frame. For example, arbitrating circuit 1405(comprising combinatorial logic, memory, and a state machine) identifiedfor a physical output port frame from one of several queues of egressbutter 1414. Each queue may correspond to a traffic class or otherpolicy values (e.g., queue for each of four traffic classes). Theidentified frame (or frame identification) is passed (1438, 1439) fromegress buffer 1414 to a media interface circuit for the physical port.Arbitrating circuit 1405 may use a round robin scheme among queueshaving a non-empty ring buffer and sufficient grants (e.g., requestedand granted by the receiving end of the link according to FC-2) topermit delivery. Arbitrating circuit 1405 may examine a PREFERENCE orPREEMPTION bit and alter arbitration to service marked frames ahead ofother frames. Arbitrating circuit 1405 may also set and monitor timersand service a queue in response to its respective timer. In an alternateimplementation, arbitrating circuit 1405 performs a method similar tomethod 702 discussed above as amended to pertain to an output physicalport as opposed to the fabric (916) and to an egress buffer as opposedto an ingress buffer (910). Memory may serve to retain a respectivegrant pool depth and TQC value for each queue (e.g., for each trafficclass and for each physical port). Thresholds and other arbitrationconfiguration values are set by processor 1424 via line 1463.

[0214] A media interface circuit serves as an interface between aphysical network connection and other portions of a port logic circuit.On output, a media interface circuit assures that signaling rules andframing rules of a desired link protocol are met for each physical port.On input, a media interface circuit derives from a frame received from alink a set of signals and information for parsing that are independentof the signaling and framing rules of the link protocol. For example, alink may conform to one of several protocols. After configuration of themedia interface circuit, a parser coupled to the media interface circuitcan parse its inputs without regard to the particular protocol of thelink. For example, media interface circuit 1406 (comprisingcombinatorial logic, memory, and state machine(s)) determines frames foroutput in response to signals received from arbitrating circuit 1405,and after being configured by frame processor 1424 for a particular linkprotocol, adds timing signals, header information, and error detectionand correction information, and sends at a suitable time, a suitableframe on a frame I/O line 1192. On input, after being configured byframe processor 1424 for a particular link protocol, media interfacecircuit 1406 receives frames from frame I/O line 1192, removes timingsignals, analyzes (and suitably strips) header information, and stripserror detection and correction information after use for determiningwhether retransmission should be requested. The results of stripping andanalysis are provided to parser 1408 via line 1446. Error detection andcorrection and retransmission requests may be logged by counters instatistics store 1426. Media interface circuit 1406 may support severalphysical ports (e.g., four) using parallel circuits, one for eachphysical port. Portions of the functions of interface signal generationand detection may be accomplished for each frame I/O line by additionalcircuitry (not shown) that may be implemented external to an integratedcircuit implementation of port logic circuit 1186. In particular, line1142 that couples host bus adapter 1140 to a port may interface directlyto a port logic circuit integrated circuit without conversion to signallevels suitable for use external to router 102. Media access controller1406 in one implementation accomplishes functions defined by FCPspecifications as levels FC-0, FC-1, and at least the FC-AL portion ofFC-2 (e.g., including state. machine(s) for buffer-to-buffer flowcontrol, point-to-point communication, dual speed 1 Gigabit/sec and 2Gigabit/sec, auto negotiation) and analogous functions for IEEE 802.31000BTX Ethernet.

[0215] An integrated circuit that implements functions of a port logiccircuit 1186 as discussed above may include four frame I/O ports perparser; one parser, one submitter, and one filter per frame processor;two frame processors serving one virtual output queue controller, oneingress buffer and one egress buffer; and four output channels to adistributing circuit. The egress buffer may have 11 queues per outputframe I/O port. The frame processors may have a 3-stage pipeline (e.g.,fetch, execute, store) similar in some respects to a RISC processor.

[0216] A parser, for each received frame, identifies portions of thereceived frame and alerts a frame processor to begin processes thatroute the frame. A parser may also prepare a query to be submitted forobtaining flow routing information, subflow routing information, orvirtual flow routing information. For example, parser 1408 (comprisingcombinatorial logic) receives information about each received frame vialine 1446 from media interface circuit 1406, stores frame information iningress buffer 1410 via line 1444, identifies particular portions of thestored frame by storing via line 1448 pointers in index 1420, providesnotice (e.g., an interrupt) to frame processor 1424 via line 1468 toinitiate processing of the frame, and provides information via line 1470to submitter 1422 for preparation of a query. In one implementation,parser 1408 and index 1420 provide frame processor 1424 with access tothe first 128 bytes of every received frame. Different frame types maylocate similar fields in different places (e.g., length of field LBA maycause different location of field FC_DL). Parser 1408 may cooperate withindex 1420 to provide uniform access to particular frame fields (e.g.,RO), accounting for differences in frame formats. Parser 1408 maydetermine a frame format, for example, with reference to SOF and TYPEand direct offsets between pointer values in index 1420 to accomplishsuitable access. In one implementation, parser 1408 classifies frames ofnetwork traffic by identifying field locations of various frame formatsin successive comparisons. For each comparison, the received frame ismasked (e.g., to select values of TYPE_ and R_CTL) and the masked valueis compared to a pattern. If the result of comparison is successful,pointers to fields are assigned values in accordance with field locationdata. For example, up to eight comparisons may be attempted by selectingin turn a tuple of mask, pattern, and field location data from memoryparser 1408. The result may provide a coded value (e.g., 3-bit protocolidentifier). This memory may be loaded from configuration data byprocessor 1424 via line 1463. By loading this memory from time to timein accordance with configuration data, each port 1192 of router 102 maybe configured to support one of a variety protocols.

[0217] As parser 1408 commits memory (e.g., in index 1420 and ingressbuffer 1410) parser 1408 provides signals 1446 that direct media accesscircuit 1406 in responding to requests for buffer-to-buffer grants.

[0218] An ingress buffer, inter alia, provides storage for informationdestined to be assembled into a frame to be sent via the fabric to aframe I/O port. Such information may have been derived from a framereceived from a link; or, may have been determined by a frame processorfor communication with a managing process or an administrating process.An ingress buffer may also provide storage for information destined tobe passed to (or as received from) a supervising process. Suchinformation may have been derived from a frame received from a link(e.g., a link service request); or, may have been determined by asupervising process for communication with a network member (e.g., alink service reply). For example, ingress buffer 1410 (comprisingcombinatorial logic and memory) receives data to be stored from parser1408 via line 1444, data to be stored from access circuits 1404 (e.g.,DMA controller 1491) via line 1443, and data from frame processor 1424via line 1456. Ingress buffer 1410 provides data from storage to dequeuelogic 1412 via line 1440, data from storage to access circuits 1404(e.g., DMA controller 1491) via line 1443, and data from storage toframe processor 1424 via line 1456. Data in storage may be organized ina ring buffer (e.g., linked lists) for each output queue. In animplementation having multiple traffic classes per output queue, data instorage may be organized in a ring buffer for each traffic class of eachoutput queue. In a preferred implementation, policy values are effectedon each flow, subflow, and virtual flow in part by enqueueing fames inaccordance with the physical port identifier (of this router) thatreceived the frame, the physical port identifier (of this router) towhich the frame is destined to be sent, and one or more policy values(e.g., one at four traffic classes).

[0219] Ingress buffer 1410 may include circuits for adding frameformatting suitable for fabric network frames. A fabric network framemay enclose the header and payload of a frame received from a frame I/Oport and thereby provide prepended header. The prepended header mayinclude destination physical port identifier or address (e.g., to beread by any egress buffer 1414 in any port logic circuit on ring 1170(e.g., fabric 213)), priority, destination port speed, source physicalport identifier or address, and flags designating, for example, whetherthis is a multicast frame.

[0220] An index provides pointers and may provide other descriptors ofsignificant portions of data stored in an ingress buffer. Descriptorsmay include starting addresses, lengths, flags, and values indicatingthe type of processing prescribed by a parser or supervising processor.For example, index 1420 (comprising combinatorial logic and memory)receives values for storage in its memory from parser 1408 via line1448. Frame processor 1424 reads via line 1462 index 1420 to addressingress buffer 1410 via line 1458 and thereby access any desired framedata. Frame data descriptors stored in index 1420 may be read byprocessor 1464 via line 1462. In one implementation, index 1420 includesmemory organized in rows (or slots). Rows may be grouped by protocolidentifier (e.g., up to 8 rows per protocol). A typical group of rows isdescribed in Table 13. TABLE 13 Field Description Pointer to R_CTL Foraccess to IU, information category; Pointer to F_CTL For determiningrole of initiator, target, originator, responder; Pointer to CS_CTL Foraccess to class of service. For example, access to class of service fora virtual transaction enables a proxy to initiate a suitable class ofservice for a nonvirtual transaction. For access to PREFERENCE bit foreffecting a policy value. Pointer to PREEMPTION bit For access toPREEMPTION bit for effecting a policy value. Pointer to TYPE Fordetermining protocol identifier, enabling access to IU data structuresof various protocols, and analysis of link service requests. Pointer toFQXID May consist of several pointers. For access to routing informationprovided in the frame. Pointer to RO Used to properly place framepayload in a cache for a proxy, cache agent, or mirror agent process.Used to determine nonvirtual LBA, page, and sector; and, whether theframe data traverses a page boundary in the nonvirtual resource. Pointerto LUN For access to a logical unit number. Pointer to OP_CODE Fordetermining type of command, type of command descriptor block. Foraccess to parametric values specified with the command. Pointer to LBAUsed to properly place frame payload in a cache for a proxy, cacheagent, or mirror agent process. Used to determine nonvirtual LBA, page,and sector; and, whether the frame data traverses a page boundary in thenonvirtual resource.

[0221] A submitter manages the presentation of queries to a memorycircuit that contains routing information or cross referenceinformation. For example, submitter 1422 (comprising combinatoriallogic) receives information from which a query (e.g., a flow query orsubflow query) is formed as described above with reference to Table 10.The query is presented on bus ROUTE 1166 and the reply is returned onthe same bus to submitter 1422. If the flow query reply indicates that asubflow query should be made, submitter 1422 prepares a subflow query.Results of flow and subflow queries are communicated to frame processor1424 via line 1472. Frame processor 1424 may provide information for aquery (e.g., a virtual flow query) to submitter 1422 via line 1474 andreceive the reply via line 1472.

[0222] In one implementation, submitter 1422 includes and maintainsqueues for communicating with parser 1408, frame processor 1424, andmemory circuit 1162. Parser 1408 pushes an entry on each of severalinput queues, each input queue corresponding to a physical port servicedby media interface circuit 1406. Frame processor 1424 pushes an entry onan input queue for each subflow lookup. When a query corresponding to anentry from an input queue is presented to memory circuit 1162, submitter1422 may pop the entry from the respective queue and push an entry ontoan output queue derived from the input queue entry and the resultreceived from memory circuit 1162. Frame processor may pop entries fromthe output queue for analysis (e.g., when a subflow flag is asserted,when a virtual flow is indicated, when the frame is a link servicerequest).

[0223] If the stall flag is asserted in a flow lookup result, frameprocessor 1424 pushes the corresponding entry from the input queue ontoa recirculation queue. Preferably, submitter 1422 includes arecirculation queue for each input queue having entries enqueued byparser 1408. By pushing an entry onto a recirculation queue, furtherprocessing of the entry by submitter 1422 will be delayed. A timerloaded from a preset value (e.g., a CSR) counts down a duration of thedelay, lapse of which dictates when a recirculation queue requiresservice. A delay may allow time for frame processor 1424 to revise fieldvalues or supply additional values that may be part of a subsequentquery, for example, revising D_ID to route the frame to managing process202 for analysis, setting a PREEMPTION flag, setting a PREFERENCE flag,or supplying a resource identifier (e.g., LUN) from memory. A delay mayresult from implementing a policy value. For example, frame processor1424 may accomplish traffic shaping by setting the stall flag in a CAM1306 result corresponding to a flow, subflow, or virtual flow asdiscussed above. Once a stall flag is set in CAM 1306, processing of asubsequently received frame will be stopped by submitter 1422 by postingthe received frames query onto a recirculation queue. Submitter 1422 maycommunicate to parser 1408 the status of recirculation queues to enableparser 1408 to inform media interface circuit 1406 that buffer-to-buffergrants should be denied due to the stall condition.

[0224] Submitter 1422 may include an arbitrating circuit to govern queueselection for submitting entries to memory circuit 1162. In oneimplementation, submitter 1422 services queues in priority from highestto lowest as: recirculation queues, flow lookup queue, and parser inputqueues (equal in priority).

[0225] Access circuits provide an interface between a frame processorand a supervising processor for example to facilitate communication oflink service requests and replies. For example, access circuits 1404include supervisor queue 1490, direct memory access controller 1491, andinterrupt logic 1492. Frame processor 1424 communicates with accesscircuits 1404 in any conventional manner indicated functionally by line1409. Supervising processor 1160 communicates with access circuits 1404via SUPRV bus 1164.

[0226] Cross reference circuits maintain associations among identifiersand other data facilitating access by a processor (e.g., a routingprocessor or a supervising processor) or access by circuits operating inparallel with a processor (e.g., a parser may post entries to adescriptor or post pointers in a frame buffer for later reference by aframe processor; dequeue logic may obtain other data for formatting aframe to be sent to the fabric by using various identifiers as indexvalues). Cross reference circuits may be implemented with anyconventional memory technology (e.g., random access memory or contentaddressable memory) and any conventional data storage technology (e.g.,ring buffer, indexed list, or hierarchical data structure). Crossreference circuits may be implemented as a central memory circuit,multiported memory circuit, or as separate independently accessiblememory circuits. For example, cross reference circuits 1425 includeframe buffer 1480, descriptors 1481, port table 636, context table 626,virtual context table 630, page table 632, and sector table 634.

[0227] Frame buffer 1480 may be used by frame processor 1424 orsupervising processor 1160 to retain information relative to receivedframes (e.g., for analysis of the frames), to reserve space for framesbeing assembled in ingress buffer 1410, or to provide space for framesprior to transfer into ingress buffer 1410. Frames in frame buffer 1480may be accessed with reference to a frame handle. In one implementation,parser 1408 assigns a frame handle to received frames and creates aworklist queue in memory accessible for reading, modifying, and deletingby parser 1408, submitter 1422, VOQC 1428, and frame processor 1424. Theworklist queue describes a frame and may serve as space for results ofanalysis and processing that relate to the frame. A worklist queue entrymay include number of slots in ingress buffer 1410 available for use bythis port, a tag to be used for a query to be submitted by submitter1422, a pointer to the respective frame in ingress buffer 1410 or inframe buffer 1480, pointers to fields of the frame or to values (e.g.,pointers) in index 1420 for access to fields of the frame, one or moreflow index values (e.g., an 8-bit identifier corresponding to an S_ID(or similar 24-bit value), to an S_ID/D_ID pair, or to an FQXID) andflags for results of analysis (e.g., virtual, nonvirtual, stalled,subflow lookup available, or link service request). A frame table listsfor each frame a starting address to locate the frame in the ingressbuffer. The frame table may be indexed by a frame identifier forconvenient reference in other tables (e.g., worklist, supervisor queue,or virtual output queue). Each row of the frame table may include valuesdescribing or limiting the purpose of storing the frame (e.g., stalenesstimestamp, reason for keeping the frame, or reason for stalling theframe).

[0228] As discussed above, portions of an ingress buffer may be used forframes received from frame I/O ports and other portions may be used forframes destined to be sent or transmitted to fabric 213. Analogously,portions of an ingress buffer may be used for data to be received by asupervising processor (copied out of an ingress buffer) and otherportions may be used for transmitting data from a supervising processor(copied into an ingress buffer). According to various aspects of thepresent invention, references to these portions may be organized toimplement ring buffers using entries in linked lists. For example, aportion of multi-purpose memory 1304 may include descriptors 1481 toimplement a transmit buffer (TXB) and a receive buffer (RXB) as in FIG.15. Multi-purpose memory 1304 includes descriptors for a transmit buffer1502 (having entries 1511 and 1512 each with starting addresses 1513 and1514 respectively) and descriptors for a receive buffer 1506 (havingentries 1531 and 1532 each with starting addresses 1533 and 1534respectively). Each descriptor includes an entry in a linked list. Eachentry includes fields for flags, target identifier, source identifier,length, and a pointer to the next entry of the list (e.g., null if thisis the last entry). Because entries in the list may be inserted ordeleted regardless of position in the list and because a search of thelist may begin with any item and proceed forwards from the last item tothe first or backwards from the first to the last, the linked list canbe used as a ring buffer. For communication with a supervisingprocessor, fields have contents as described in Table 14. TABLE 14 Fieldof Entry of a Descriptor Description Flags Values set or cleared tofacilitate search of the linked list. Suitable values may indicate“sent”, “acknowledged”, and/or processing “complete”. List maintenancemay be facilitated by reading flag values (e.g., indicating that a listentry may be reused for another purpose, or freeing the list entry topermit use of memory for any purpose). Target A start address forcontent to be written by DMA controller 1491. For a transmit bufferentry (e.g., 1511) the target address is typically an address of ingressbuffer 1510 (e.g., payload 1521 of TXB 1504). For a receive buffer entry(e.g., 1531) the target address is typically an address of data memory1208. Source A start address for content to be read by DMA controller1491. For a transmit buffer entry (e.g., 1511) the source address istypically an address of data memory 1208. For a receive buffer entry(e.g., 1531) the source address is typically an address of ingressbuffer 1510 (e.g., payload 1541 of RXB 1508). Length The number of bytes(or other suitable measure) to be copied by the read or write operationof DMA controller 1491. Next A pointer to the next list entry or null ifnone. A tail pointer value may be set to the start address of an entryhaving a null NEXT field value (e.g., 1512 and 1532). A head pointervalue may be set to the start address of a first entry in the list. Forexample, a TXB head pointer may specify address 1513; and the value ofNEXT in entry 1511 identifies the starting address 1514 of entry 1512.An RXB head pointer may specify address 1533; and the value of NEXT inentry 1531 identifies the starting address 1534 of entry 1532.

[0229] DMA controller 1491 may refer to a head and a tail pointer foreach buffer (TXB and RXB). Head and tail pointers may be specified bysupervising processor 1160 when setting up a DMA transfer. Head and tailpointers may refer to the first and last entry in the buffer. When anentry has been copied by DMA controller 1491, DMA controller 1491 mayrevise the head pointer to the value of the NEXT field in the entry thathas been completed. When DMA controller 1491 detects that a tail pointerfor any buffer is not equal to the head pointer for that buffer, DMAcontroller 1491 may perform the specified copy operations (e.g., oneoperation per entry) until the head and tail pointers are equal.

[0230] To simplify maintaining multiple CAM associated data records thatrefer to a router port identifier (or virtual output queue), CAMassociated data includes logical port identifiers. The conversion of alogical port identifier to one or more physical port identifiers isaccomplished by frame processor 1424, VOQC 1428, or egress buffer 1414with reference to a port table. A port table 636 entry may includefields as described in Table 15. Multiple entries for the same logicalport identifier may be used to specify a broadcast or multi-castrouting. TABLE 15 Field of Port Table 636 Description Logical Anindirect reference to a physical port of the router. router portidentifier Physical An identifier of an output physical port of therouter. router port May be a frame I/O port (e.g., an N-port, an E-port,identifier or a port to managing processor 1112 for communication with aprocess performed by the managing processor). This field may identify atraffic class and output queue emptied via a physical router port tonetwork 101.

[0231] A context table provides storage for port identifiers and policyvalues to be associated with all communication (e.g., sequences) of thetransaction. A context table 626 entry may include fields as describedin Table 16. TABLE 16 Field of Context Table 626 Description TransactionAn identifier assigned by the requester or a proxy acting as arequester. For a identifier SCSI over Fibre channel protocol, therequester may be an initiator and the transaction identifier may be thevalue of the OX_ID field. Source port An identifier of the port fromwhich a request of the transaction originated (e.g., identifier aninitiator's port identifier or network address). The source portidentifier may be the value of the S_ID field in a received frame.Destination An identifier of the port to which a request of thetransaction is directed (e.g., a port identifier participant's port, atarget port identifier, or network address). The destination portidentifier may be the value of the D_ID field in a received frame. QoSPolicy values to use for this transaction (e.g., including specificationof traffic class). The QoS as entered into the context table may becopied from or derived from field values of the received frame includingCS_CTL. The QoS value may be derived from routing information includingtraffic class that has been associated with this requester (e.g., S_IDfield value) or a participant (e.g., D_ID field value). LogicalSpecifies a route in accordance with one or more rows of port table 636.The output port value for logical output port may be determined inaccordance with the value of the S_ID field, the physical input port ofthe router that received the frame, and/or the traffic class. Whenrouting information defines several output ports and/or traffic classes,the routing processor determines one output port and traffic class(e.g., using conventional methods such as shortest path) and may specifythe virtual output queue here to implement that route. Statistics Anidentifier of a counter to be conditionally incremented when a frame ofthis counter transaction is processed. Whether or not to increment thecounter may depend identifier on whether a time of day (or a portion ofa time value) falls within a range defining a period for collectingstatistics. Flags A composite value that may include: a value to use inplace of CS_CTL (e.g., for implementing a policy value); and/or a valuethat indicates one or more of the following: whether this transaction isstalled, or whether to drop frames of this transaction (e.g., set inresponse to a link service request to cancel the task or transaction, orset to implement a security function).

[0232] A virtual transaction is a transaction recognized by the routeras referring to a virtual participant (e.g., a virtual member, virtualresource, or portion of a virtual resource). For a SCSI over Fibrechannel protocol, a transaction is recognized as a virtual transactionwhen: (a) a frame has a value in the D_ID field that is recognized (fromrouting information or a predetermined range of values) as a virtualmember; (b) a frame has a value in the LUN field that is recognized(from routing information or a predetermined range of values) as avirtual resource (e.g., storage or process); or (c) a frame has a valuein an address field that is recognized (from routing information) as avirtual address (e.g., virtual LBA for storage, virtual page (such aspart of an LBA), virtual sector (such as part of an LBA), or an objectreference).

[0233] In one implementation, the D_ID field provides a composite valueincluding an identifier of the router (e.g., a domain), and anidentifier of a virtual member. For example, a 24-bit D_ID field [23:0]having bit 15 zero provides a nonvirtual destination port identifier inbits [14:8] and a loop port identifier (e.g., AL_PA) in bits [7:0]. AD_ID field having bit 15 set provides a virtual destination portidentifier in bits [7:0]; and, bits [14:8] may be used for routing onfabric 213.

[0234] A virtual context table 630 entry may include fields as describedin Table 17. TABLE 17 Field of Virtual Context Table 630 DescriptionRequester An identifier of the requester that originated the virtualtransaction. For example, for a FCP_CMND frame of a virtual transactionfrom an initiator, the value of the S_ID field. When the routeroriginates frames of the virtual transaction back to the initiator(e.g., in response to frames received from a nonvirtual target), thevalue of the D_ID field in the frame originated back to the initiatorwill be assigned by the router from the Requester entry in this row ofthe virtual context table. Virtual An identifier assigned by therequester that identifies this virtual transaction. For transactionexample, the value of the OX_ID field. The virtual transactionidentifier is used identifier as an index into this virtual contexttable 630 to obtain one or more rows of this virtual context table 630.Virtual An identifier assigned by the router for use in a virtualtransaction (e.g., participant's VRX_ID). transaction identifierNonvirtual An identifier (e.g., determined from routing information) ofa nonvirtual participant participant of a nonvirtual transaction used toimplement an intent of the virtual transaction. May be used as the valueof an D_ID field in a frame of such a nonvirtual transaction (e.g.,directed to the nonvirtual target corresponding to the virtual target ofthe virtual transaction). Nonvirtual An identifier of a nonvirtualtransaction to be conducted to accomplish an intent transaction of avirtual transaction. Typically assigned by a routing processor (e.g.,acting as identifier requester, initiator, or originator). Typicallyassigned when the virtual transaction is to be routed (e.g., the firstrouting processor between an initiator and a target having routinginformation sufficient for that routing processor to recognize thetransaction as a virtual transaction). The nonvirtual transactionidentifier (e.g. NVOX_ID) may be used as the value of the OX_ID field ofa frame of a nonvirtual transaction. The nonvirtual transactionidentifier is used as an index into this virtual context table 630 toobtain one or more rows of this virtual context table 630. Nonvirtual Anidentifier assigned by a participant of a nonvirtual transaction (e.g.,participant's NVRX_ID). The participant's transaction identifier may bedetermined from a transaction frame directed back to an initiator (e.gan RX_ID field of a response). identifier Nonvirtual An identifier of aportion of a nonvirtual transaction. A SCSI I/O comprising sequencesequences corresponds to a transaction. Nonvirtual sequence identifiermay be identifier assigned by a proxy or a routing processor (e.g.,NVSEQ_ID). Nonvirtual An identifier of a relative offset that describesthe offset into a buffer of the data offset being conveyed by thepayload of this frame. For example, a virtual transaction may bedescribed by a relative offset (e.g., the value of field RO in aFCP_DATA frame). The corresponding nonvirtual transaction may beconducted independently of the virtual transaction (e.g., in a deliveryorder specified by the nonvirtual target). A payload in the nonvirtualtransaction may therefore be identified by a nonvirtual offset (e.g.,NVRO). Flags A composite value that may include whether to discard theframe (e.g., to enforce access control or abort a task), whether toroute the frame to a proxy process, or whether to pass the frame to asupervising process. Timestamp A value indicating time when this row wascreated. Used to flush stale rows of this virtual context table 630.

[0235] According to various aspects of the present invention, a virtualidentifier is associated with a nonvirtual entity so that reference tothe virtual identifier accomplish communication affecting the nonvirtualentity. This association may be implemented as a virtual memberidentifier associated with a nonvirtual member identifier (e.g., amember-to-member association). Alternately, the association may beimplemented with member/resource-to-member/resource association, amember/resource/address-to-member/resource/address association, amember/object_reference-to-member/object-reference association, orpermutations of these. These associations may be one to many (e.g.,facilitating redundancy in storage or processing). When a storageresource address includes further segmentation, (e.g., a logical blockaddress may include a page, sector, and block offset), a reference to avirtual sector may affect one or more nonvirtual sectors.

[0236] In one implementation, storage virtualization is implementedusing one or more page tables and one or more sector tables. Forexample, each virtual resource identifier may be associated with onepage table that includes one or more rows. Each page table row isassociated with one sector table that includes one or more rows.

[0237] In an alternate implementation, a query for routing informationmay result in a maximal match of the query tag that includes in order:member identifier, resource identifier, page address, sector address,and block address. In a preferred implementation, described below, theblock address is omitted and storage virtualization is accomplished tothe sector level.

[0238] A page table stores a one-to-many association between anidentifier of a virtual storage address and a nonvirtual storageaddress. A page table 632 entry may include fields as described in Table18. When routing information provides a direct reference (as opposed toan indexed reference) to a particular page table, the virtual resourceidentifier field may be omitted. TABLE 18 Field of Page Table 632Description Virtual An identifier of a virtual resource for which acorresponding nonvirtual page resource table has been defined.identifier Virtual Page An identifier of a page as referred to in avirtual transaction. For example, a Address CDB of a virtual transactionmay include a value in the LBA field comprising virtual page address (aswell as a sector and a block address). Virtual An identifier of thefirst sector of a list of sectors described in a sector table SectorList describing nonvirtual sectors that implement the virtual page. Eachsector of the list may be located on a different nonvirtual resourceand/or at different pages of a nonvirtual resource. Valid A flagindicating whether this row of page table 632 is valid. Permitsefficient reuse of a row.

[0239] A sector table stores an ordered list of sectors that comprise apage. For example, if a virtual page comprises 512 sectors, then asector list associated with that virtual page (e.g., a row of a pagetable, discussed above) includes 512 rows, the first row correspondingto the first sector of the virtual page, and so on. A sector table 634entry may include fields as described in Table 19. The virtual sectoraddress field may be omitted from sector table 634 when the order ofsectors is maintained by design (e.g., sequential order 0-511). Thenonvirtual sector address field may be omitted when access by nonvirtualsector address is not desired. TABLE 19 Field of Sector Table 634Description Virtual sector The virtual sector address of a virtual page.May be used as an index to obtain address associated values from thisrow of sector table 634. Nonvirtual The nonvirtual sector addressassociated with the virtual sector address of a sector virtual page. Maybe used as an index to obtain associated values from this row address ofsector table 634. Nonvirtual An identifier of the nonvirtual memberimplementing this nonvirtual sector. For member example, a value (e.g.,NVD_ID) used in the D_ID field or a nonvirtual identifier transaction.Nonvirtual An identifier of the nonvirtual resource implementing thisnonvirtual sector. For resource example, a value (e.g., NVLUN) used inthe LUN field of a nonvirtual identifier transaction. Nonvirtual Anaddress that identifies nonvirtual data for this virtual sector. Forexample, a address value (e.g., NVLBA) used in the LBA field of anonvirtual transaction. Nonvirtual The number of sectors (e.g., startingsector number, ending sector number, bounds and/or quantity of sectors)in the nonvirtual LBA. May differ from the number of sectors in thevirtual LBA. May be used to determine whether a virtual transaction willcross a page boundary. Control A composite value indicating: whether thenonvirtual sector is part of a snapshot, part of a mirror, or isassociated with a cache. Routes Routing information (or one or morepointers to routing information) describing alternate paths to thenonvirtual sector. Each alternate route may designate an output queueand traffic class.

[0240] An output queue presents frames to the fabric. For supportingmultiple output queues, a frame may be copied to a region of memorydesignated with a suitable priority and/or traffic class. Alternatively,a so-called virtual output queue may include pointers to the frame as itmay already exist in a memory that serves a function different from anoutput queue. For example, output queue 1437 includes virtual outputqueue controller (VOQC) 1428 and dequeue logic 1412. Output queue 1437refers to the frame as it exists in ingress buffer 1410, therebyavoiding the time and resources needed to maintain a copy of the framein a memory different from the ingress buffer. Dequeue logic 1412(comprising combinatorial logic) presents frames to distributing circuit1402 via line 1434 (or portions of frames such as identifiers andpayloads as discussed above with reference to distributing circuit1402). Dequeue logic 1412 is directed by command signals received fromVOQC 1428 via line 1442. Commands include directives to format datapointed to by pointers maintained by VOQC 1428 to form frames asdirected, send frames, drop frames (e.g., to interrupt a link inresponse to a suitable link service request or exceptional condition),and stall queues (e.g., as discussed above with reference to FIG. 9).

[0241] VOQC 1428 may include combinatorial logic and/or one or morestate machines to perform methods discussed above with reference toFIGS. 9 and 10 for each output queue. VOQC also receives flow controlsignals from distributing circuit 1402 via line 1436. If operation ofarbitrating circuit 1405 and egress buffer 1414 result in a buffer fullbeyond a threshold, egress buffer 1414 provides flow control signals todistributing circuit 1402 via line 1432, as discussed above.Distributing circuit may respond to such flow control signals and toexceptional conditions (e.g., loss of synchronization or timing delayassociated with receiving signal RING-I or providing signal RING-O, lackof sufficient grants for sending, initialization, reinitialization, orhigh error rates) by asserting flow control signals to VOQC 1428 vialine 1436.

[0242] Output queues may be implemented as ring buffers in ingressbuffer 1410. When permitted by flow control signals 1436 and accordingto a method of arbitrating among sources of similar priority (e.g., asdiscussed above), VOQC 1428 identifies to dequeue logic 1412 via line1442 data for sending to the fabric from a ring buffer in ingress buffer1410. Upon successful processing of the identified frame, dequeue logic1412 may adjust the ring buffer pointers to remove the identified framefrom the queue. A region of memory removed from a ring buffer may bereallocated to any other function provided by ingress buffer 1410. Byallowing reallocation of ingress buffer memory, frames of varying lengthmay be accommodated, queues of varying capacity may be accommodated,queue stalls may be implemented by allowing a ring buffer to grow insize, flow controls such as buffer grants may be implemented, andarbitration may be accomplished based on information associated witheach output queue including identifiers related to flow, subflow,virtual flow, destination, protocol, resource, traffic class, andpriority.

[0243] The number of virtual output queues maintained by VOQC mayinclude multiple queues. for the same destination output physical portidentifier. For example, in one implementation, a frame to be enqueuedfor output to fabric 213 is pushed into a queue corresponding to thesource physical port identifier from which the frame was received bythis port logic circuit (e.g., a port logic circuit may serve 4 portsfor input), and further corresponding to a traffic class. Consequently,an arbitrating circuit for one physical output port arbitrates among alarge number of queues. For example, when a port logic circuit serves 4physical input ports (local to this port logic circuit), recognizes 4traffic classes, and routes frames on fabric 213 to up to 20 physicaloutput ports (e.g., 16 frame I/O ports in router 102, one port to amanaging process (e.g., 204), and one multicast port), VOQC manages atotal of 320 queues. Each of 20 arbitrating circuit selects from 16queues.

[0244] An entry in a virtual output queue may include the valuesdescribed in Table 20. TABLE 20 Field of virtual output queue entryDescription Frame to output pointer to a frame in ingress buffer 1410;flag for CRC regeneration; Principal output queue physical or logicaloutput port identifier; port speed to be used for the output port;priority (e.g., if set, arbitration according to traffic class may besuperceded); Multicast multicast destination identifier (e.g., D_ID);Statistics statistics counter identifier; Secondary output queuephysical or logical output port identifier; port speed to be used forthe output port; priority (e.g., if set, arbitration according totraffic class may be superceded); Miscellaneous midswitch stageidentifier;

[0245] The secondary queue, if specified, may direct that a copy of theframe be sent to a managing process 204, to an administrating process202, or to another resource. The managing process, administratingprocess or resource may appear (if not intentionally made invisible) asa target (e.g., a virtual target) to the source of the frames. Sending acopy of a frame to a managing process may facilitate configurationmanagement by process 406, or report generation by process 410 (e.g.,accumulation of traffic statistics in addition to statistics reported byrouters 102-105). Sending a copy of a frame to an administrating processmay facilitate monitoring for security purposes. Frames to be sent to asecondary output queue may be selected based on traffic statistics, oron type of frame. For example, frames writing a primary data store (notreading the primary data store) would be sent to a mirror data store.Sending frames to a managing processor that hosts a mirror agent (426)facilitates receiving frames in a first order preferred for the firstinitiator; and acting as an initiator for serving the mirror resource ina second order preferred for operation of the mirror resource. Themirror agent may perform initiator and data transfer functions analogousto a proxy process, discussed above.

[0246] A statistics store accumulates counts of traffic statistics asdescribed above. For example statistics store 1426 (comprisingcombinatorial logic such as counters, and memory) receivesspecifications for what statistics to accumulate, how to accumulatethem, and provides status and results to frame processor 1424 via line1460. Statistics store 1426 receives notice of events for possiblecounting from media interface circuit 1406, arbitrating circuit 1405,parser 1408, dequeue logic 1412, and virtual output queue controller1428. Counts may be restricted to events related to a particular subflowof a link and/or to a particular protocol used on a link. For example,counts may be accumulated for frames exceeding a threshold length thatare received on a particular physical port, are directed to a particularsubnetwork resource (e.g., process or device), and contain indicia of aparticular upper level protocol (e.g., CORBA, SMTP, or VI), upper levelfile system (e.g., UNIX, WINDOWS), or upper level file type (e.g.,images such as jog, movies such as .mpeg, audio such as .wav, text suchas .doc, database such as .index). Counts may be accumulated forintervals as directed by frame processor 1424. Intervals may bespecified at random, of random duration, or at particular times andparticular durations. The start time for collecting a specifiedstatistic may also be set in accordance with the occurrence of an event(e.g., another statistic counter has exceeded a threshold).

[0247] Statistics counters may cooperate with values recalled from CAM1306 to determine whether an event should be tallied. For example, CAM1306 may provide one or more values that specify a sampling window(e.g., hourly, daily, weekly; with a relative start time (8:15 a.m. eachday), duration, and/or relative end time (8:30 a.m. each day)) duringwhich an event should be tallied or a frame sampled for purpose ofdetermining whether a countable event is indicated by the contents ofthe frame. Current time of day may be compared to the values specifyingthe sampling window to determine whether to ignore the frame, count it(e.g., as a unit or accumulate its length), or analyze it for possiblestatistics.

[0248] A routing processor includes any stored program computer circuitand/or state machine that performs a routing process 208 as describedabove with reference to FIG. 2. A routing processor 1161 may include aport logic circuit and interfaces to a supervising processor and to amemory circuit. Alternately, a routing processor 1161 may furtherinclude a memory circuit or exclusive use of a portion of a memorycircuit. For example frame processor 1424 in one implementation performsmethods described above with reference to FIGS. 2 and 6, and portions ofFIGS. 7-10 that are not implemented in separate circuits for parallelprocessing. Frame processor 1424 includes EPM to enable downloadingprograms to be executed by routing engines. Such programs may differamong routing engines of router 201, for example, to implement differentprotocol support on different frame I/O ports or at different timesduring operation of the same frame I/O port. Frame processor 1424 hasaccess to shared memory 1162 (e.g., for read, write, fetch, indirectaddressing, stacks, and heaps) via ROUTE bus 1166.

[0249] To process a link service request received from any frame I/Oport, parser 1408 indicates to frame processor 1424 that a link servicerequest has been placed in ingress buffer 1410 by signals on line 1468.Alternatively, frame processor 1424 may determine that a frame receivedis a link service request by reading portions of ingress buffer 1410identified by index 1420. Frame processor 1424 may create an entry insupervisor queue 1490 to notify supervising processor 1160 of thereceived link service request. Supervising processor 1160 may respond toan interrupt generated by interrupt logic 1492 or may periodically readsupervisory queue 1490 to discover the pending queue entry. Supervisingprocessor 1160 may then set up DMA controller 1491 and interrupt logic1492 to copy suitable portions of the frame from ingress buffer 1410 todata memory 1208 for convenient access during processing of the linkservice request. The region of ingress buffer 1410 used by the frame maythen be freed for other use as discussed above. The entry in supervisorqueue 1491 may also be freed.

[0250] Supervisor queue 1490 may be implemented as a ring buffer orarray in any suitable memory circuit. For example, memory for supervisorqueue 1490 may be allocated from a portion of ingress buffer 1410 orfrom multi-purpose memory 1304 (e.g., a reserved region or a regionshared by multiple frame processors). When placing entries in supervisorqueue 1490, a priority value may be associated with the entry so thatprocessing by supervising processor 1160 may respond to higher prioritylink service requests that enter the queue in time after lower prioritylink service requests. Priority may be determined with reference to oneor more of the following: identifiers of a routing processor, a type oflink service request, a flow, a subflow, a virtual flow, a resource, ora protocol.

[0251] To process one or more link service replies to be sent to anyframe I/O port(s), a managing process, and/or an administrating process,supervising processor 1160 may set up DMA controller 1491 and interruptlogic 1492 to copy suitable portions of one or more frames from datamemory 1208 to ingress buffer 1410. If any frame written by DMA isplaced in a region of ingress buffer 1410 monitored by frame processor1424, frame processor 1424 may act on the frame in any manner discussedabove (e.g., to accomplish routing a flow, subflow, or virtual flow) Ifany frame written by DMA is placed in an output queue managed by VOQC1428, the frame is passed to the fabric as discussed above whereupon theframe is received from the fabric by a suitable egress buffer anddelivered via a frame I/O port as discussed above. Supervising processor1160 may respond to an interrupt generated by interrupt logic 1492 ormay periodically read supervisory queue 1490 to discover completion ofprocessing of frames to facilitate subsequent DMA of further frames asdesired.

[0252] As discussed above, a transaction (e.g., an input/output (I/O) oran exchange) for accomplishing a data transfer between members mayinclude either a read operation (the subject data being from theparticipant) or a write operation (the subject data being to theparticipant). Such a transaction is generally referred to as a R/W I/O(e.g., the terms transaction, I/O, and exchange, referring loosely andgenerally to either a read or a write operation). According to FibreChannel and SCSI protocols, a R/W I/O includes transactions between aninitiator and a target that employ frames (or IUs) identifiable asFCP_CMND, FCP_XFER_RDY, FCP_DATA, and FCP_RSP. According to variousaspects of the present invention, a routing processor implements methodsof routing R/W I/Os for nonvirtual and for virtual transactions. Forexample, frame processor 1424 detects frames of nonvirtual non-R/W I/Osand identifies them for processing by supervising processor 1160. Frameprocessor 1424 detects frames of virtual non-R/W I/Os and routes themfor processing by a proxy process of managing processor 1112.

[0253] A method of processing frames according to various aspects of thepresent invention may include any suitable combination of the followingoperations: receiving a frame from a network; determining in a routingprocessor whether the received frame is a data frame (e.g., part of adata transaction); if the received frame is not a data frame (e.g., partof a control transaction), identifying the frame for processing (e.g.,by a supervising processor for nonvirtual control frames; and by a proxyprocess for virtual control frames); if the received frame is a dataframe, determining a resource identifier referred to by a R/W operationof the data transaction; determining a nexus (e.g., an I_T_L nexus orI_T_L_Q nexus) of the R/W operation, recalling a policy value associatedwith the nexus; enqueueing data for the R/W operation in a first bufferin accordance with the policy value; dequeueing data from the firstbuffer for transfer on a fabric by arbitrating among queues inaccordance with a historical value; adjusting the historical value inaccordance with the amount of data transferred on the fabric; receivingdata from the fabric; enqueueing data received from the fabric in asecond buffer; and dequeueing data from the second buffer for transferto the network. Such a method may be performed by the cooperation of arouting processor, managing processor, and supervising processor. Forexample, login, proxy, and error condition handling operations may beaccomplished by managing processor 1112 in cooperation with a routingprocessor and supervising processor, as discussed above.

[0254] In the following discussion, a SCSI I/O R/W sequence is anexample of a R/W I/O series; other SCSI sequences are examples of anon-R/W I/O series.

[0255] For example, a series of messages 1600 of FIG. 16 includes anon-R/W I/O series 1601, a nonvirtual R/W I/O series 1621, and a virtualR/W I/O series 1631. In the non-R/W I/O series 1601, an initiator (e.g.,a nonvirtual member of network 101) 1660 sends at time 1602 a message“A” (e.g., a link service request). Message “A” is addressed to a router(e.g., router 102) using a well known address. Routing processor 1661(e.g., having a port logic circuit 1186 for a suitable number of ports,a memory circuit 1162, supervisor bus 1164, and route bus 1166)cooperates with supervising processor 1160 as described for link servicerequests in Table 23, e.g., sending message “B” at time 1604. When alink service request affects the state of a proxy or requiresinformation maintained by a managing process as discussed above,supervising processor 1160 sends at time. 1606 a message “C” to managingprocessor and receives a response message “D” at time 1608. Messages “C”and “D” are conveyed by LAN 210, 1132. Supervising processor 1160, onreceipt of status or information from message “D”, sends at time 1612message “E” to routing processor 1661. A response message “F” is sent byrouting processor 1661 to initiator 1660 at time 1612. Messages “B” and“E” are conveyed by bus 212, 1164. Messages “A” and “F” are conveyedthrough fabric 213, 1170, 1402.

[0256] In the nonvirtual R/W I/O series 1621, no messages refer tovirtual ports. Initiator 1660 sends at time 1622 a message “G” (e.g., anFCP_CMND to read data from a target) that is routed by routing processor1661 as message “H”, sent at time 1624 to target 1662. Target 1662responds by sending at time 1626 message “I” that is routed by routingprocessor 1661 as message “J” sent at time 1628 to initiator 1660. Whenthe non-R/W I/O is one sequence of a transaction, the remainingsequences (e.g., FCP_XFER_RDYs, FCP_DATAs, and FCP_RSP, andacknowledgement frames) would follow the same processing path G-H-I-J.As discussed above, architecture 200 of router 201 accomplishesnon-blocking routing for, inter alia, nonvirtual R/W I/Os.

[0257] In the virtual R/W I/O series 1631, messages “K” and “P” refer toa virtual target as opposed to nonvirtual target 1662. Initiator 1660 attime 1632 sends message “K” addressed to a virtual target (not shown).If routing processor 1661 routes the virtual R/W I/O message “K” at time1634 to a proxy process 418 using a well known address of the proxyprocess, the proxy process (hosted by managing processor 1112) at time1636 responds with message “M”. Routing processor 1661 may route message“M” as message “N” addressed from the proxy process to a nonvirtualtarget 1662 at time 1638. A message “M” may be addressed to initiator1660 and so be routed back to initiator 1660 as message “P”. On theother hand, when no assistance from proxy process is desired, routingprocessor 1661 may respond to message “K” by sending message “N”addressed to target 1662 from the proxy process. When target 1662responds, it sends at time 1640 message “O” addressed to the proxyprocess. Routing processor 1661 intercepts message “O” and, withoutcommunication with the proxy process, routes message “P” at time 1642 toinitiator 1660 addressed from the virtual target (not shown). Messages“L” and “M” are nonvirtual messages 1635 referring to a suitable proxy.In the message series “K”, “N”, “O”, “P” messages “K” and “P” arevirtual and messages “N” and “O” are nonvirtual. The routing of messages“N” and “O” differs from the routing of messages “H” and “I” in that theidentifiers for source and destination in messages “G”, “H”, “I”, and“J” are unchanged during routing. By contrast, the routing of messages“N” and “O” may include saving the source and destination identifiersfrom message “K” and rewriting the source and destination identifiers toform so-called redirected messages “N” and “O” 1339 by routing processor1661.

[0258] A proxy process of managing processor 1112 acting as an initiatormay send 1629 a message (e.g., discovery, port log-in, process log-in,or SCSI commands such as RESET_LUNS) to target 1662 (not shown). Target1662 may reply to such a command by sending a message (not shown) to theproxy (e.g., completion status).

[0259] Processing for representative control frames and data frames isdescribed in Table 21; FCP_CMND, FCP_XFER_RDY, and FCP_DATA sequencesrepresent data transactions having data frames. Other sequences in thetable represent control transactions having control frames. TABLE 21Received Frame Description of processing FLOGI (fabric login as Routingprocessor: identify frame (1702, 1704) as a link service defined, e.g.,in FC-FS) request; identify frame to supervising processor (1706).Supervising processor: reply to FLOGI and accept service parametersaccording to requested class of service. RTIN (request network Routingprocessor: identify frame as link service request, identify topologyinformation as frame to supervising processor. defined, e.g., in FC-FS)Supervising processor: reply to RTIN with identifiers of members andresources. PLOGI (port login as Routing processor: for nonvirtualdestination identifier, identify defined, e.g., in FC-FS) the frame as alink service request, identify frame to supervising processor. Forvirtual destination identifier, pass the frame to the correspondingproxy in the managing processor. Supervising processor: prepare suitablereply. Managing processor: initiate second PLOGI to nonvirtual targetthat corresponds to the virtual target indicated in the first PLOGI;respond to the first PLOGI in accordance with the result of the secondPLOGI from the nonvirtual target. PRLI (process login as Routingprocessor: for nonvirtual destination identifier route as defined, e.g.,in FCP-2, not conventional traffic to the nonvirtual destination. Forvirtual handled herein as a link destination identifier, pass the frameto the corresponding proxy in service request) the managing processor.Managing processor: perform operations analogous to PLOGI, discussedabove. REPORT LUNS (request Routing processor: for nonvirtualdestination identifier route as for logical unit numbers as conventionaltraffic to the nonvirtual destination. For virtual defined, e.g., inSPC-3) destination identifier, pass the frame to the corresponding proxyin the managing processor. Managing processor: reply with list of LUNs(nonvirtual and virtual) that are permitted to be accessed by thisrequester; may defer storing LUNs in CAM 1306 until first access attemptis recognized. FCP_CMND (FCP header Routing processor: for nonvirtualdestination identifier route as with SCSI command CDB conventionaltraffic to the nonvirtual destination. For virtual in payload asdefined, e.g., destination port identier, prepare a forward frame toroute in place in FCP-2) of the received frame as described, inter alia,in FIGS. 17-20. FCP_XFER_RDY (transfer Supervising processor: noinvolvement except for initialization ready sequence with and updatingmaps. response data as defined, Managing processor: no involvementexcept for initialization and e.g., in FCP-2 and SBC-2) updating maps.FCP_DATA (data transfer for a read or write of the target as defined,e.g., in FCP-2 and SBC-2)

[0260] A routing processor provides nonblocking routing of R/W I/Os. Amethod 1700 of FIGS. 17-20 provides routing of non-R/W I/Os, nonvirtualR/W I/Os and virtual R/W I/Os as follows. Routing processor 1161recognizes a frame received from network 101 via a frame I/O port as R/WI/O (1702, 1704); recalls a flow lookup from CAM 1306 (1716) and ifincomplete or missing (1718), gets a supervising processor 1160 toanalyze the frame, specify a route, or drop it (1706-1714). If thesubflow flag is set in the result of the flow query(1720), the routingprocessor does subflow lookup (1722) from CAM 1306 and reports errors tothe supervising processor (1724, 1706-1714) possibly stalling frame insubmitter queue awaiting CAM update by supervising processor.

[0261] Context and virtual context may be stored locally (e.g., inmemory accessible to a frame processor of a port logic circuit, forexample, on the same substrate as the frame processor), stored inmulti-purpose memory 1304, or stored in RAM 1312. When context table 626and/or virtual context table 630 are stored locally, a frame received ata first port logic circuit is tested as to whether the routing processorhas access to context (1726); and, if context is stored elsewhere, theflow and subflow results are used to build a forward frame (1728),marked for further processing by another routing processor (1730) wherethe context is available. Otherwise, it is determined whether thecontext is already available; and, if not, a new entry for context table626 and/or virtual context table 630 is created (1734) in the localmemory or where context is stored.

[0262] Assuming that local context and/or virtual context is available,such may be revised with information parsed from the received frame. Ifa LUN is specified in the CDB (e.g., FCP_CMND frame) (1802), the routingprocessor sets subflow flag (1804) and stores modified results (1806) incontext table 626. If the frame includes an RX_ID value from the target(e.g., an ACC to FCP_CMND, or an FCP_XFER_RDY) or proxy for the virtualtarget (1808), the routing processor stores (1810) the RX_ID in contexttable (626). If there were CAM hits on the lookups, the routingprocessor tests the CAM result flag for virtual (1812). If nonvirtual,an update of the context table with tuple of S_ID, D_ID, LUN, LBA,OX_ID, and RX_ID is accomplished. The flow, subflow, and context tableare then used to route frame (1814) to an output queue (1816) per S_ID,router output port identifier and traffic class.

[0263] If the received frame is determined to be virtual (e.g., eitherthe flow or subflow lookups indicate the D_ID is associated with avirtual target) and if no suitable nonvirtual transaction identifier(1902) is in virtual context table 630, the routing processor creates atuple of virtual transaction identifier (e.g., original OX_ID frominitiator 1660) and new nonvirtual transaction identifier (NVOX_ID) andstores (1904) as a new entry in virtual context table 630. If there isno known proxy (1912), the routing processor routes the frame tomanaging processor 1112 for analyzing, revising tables, or dropping theframe. If the frame is virtual and NVOX_ID is available from virtualcontext table 630 (e.g., from FCP_XFER_RDY, or ACK), then OX_ID, LBA andRO may be used as an index to the virtual context, page, and sectortables to determine nonvirtual destination (NVD_ID), nonvirtualinitiator (e.g., a proxy NVS_ID), nonvirtual NVLBA, and whether theamount of data to be read or written will cross a page boundary (1906,1908). If no page boundary will be crossed, the routing processormodifies (1910) the frame to appear as sent from a proxy in a nonvirtualtransaction to the nonvirtual target.

[0264] For both nonvirtual and virtual processing, after a frame for thefabric has been prepared (1738, 1910, or 1914), the routing processorenqueues the frame (1816) to the fabric and later this or anotherrouting processor receives the frame from the fabric (2002). If theframe received from the fabric is marked (1730, 2004) as requiringapplication of virtual context at this routing processor, context andvirtual context tables are used to modify (2006) the frame to appear tohave been sent by the virtual target to the initiator; else the frame issimply passed (2008) to the output port as for a message (“F”, “H”, “J”,“L”, “N” or “P”) directed to a nonvirtual destination.

[0265] A supervising processor cooperates with a routing processor asfollows. If the supervising processor is passed a frame for which a CAMhit is missing, the supervising processor uses the S_ID to get an ACL.If a value for D_ID and LUN are in the ACL (possibly not in CAM becauseno prior access attempt), the supervising processor updates theappropriate CAM with LUN; else, if D_ID and LUN are not in the ACL, thesupervising processor drops the frame, implementing security of access.

[0266] A fabric according to various aspects of the present inventionprovides full-mesh communication using point to point connections. Nodesof the fabric are joined by point to point connections in a topologysimilar in some ways to a star and in a physical arrangement similar insome ways to a ring. Each node provides a slice of the fabric circuitry.According to various aspects of the present invention, a slice capableof being inserted into a ring coupling a maximum number of frame I/Oports may be used in a ring of any lesser number of frame I/O ports,eliminating costly development of fabric circuits for different routerseach having a different number of frame I/O ports. The fabric mayinclude a printed circuit layout that need not be revised for productionof various models of routers having support for different numbers offrame I/O ports. An implementation of a fabric according to variousaspects of the present invention may have any maximum number of nodeslimited perhaps by transmission delays and timing differences that maydevelop between nodes. Each segment of a fabric may comprise a point topoint transmission line driven by one transmitter and terminated by onereceiver with suitable impedance matching termination circuitry.

[0267] In one implementation of fabric 213, for example fabric 2100 ofFIG. 21, full mesh communication is provided between all ports at eachof five fabric nodes. Fabric 2100 includes five circuits 2101-2105 (oneat each fabric node), each having port I/O circuitry (PIOC) that may besimilar in some respects to circuitry described above with reference toport logic circuit 1186. Each PIOC provides an interface to a pluralityof frame I/O ports (not shown). In the simplified functional blockdiagram representation of fabric 2100 in FIG. 21, a frame sent to thefabric from PIOC 2111 at node 2101 is coupled to node 2102 by segment2121, is then coupled to node 2103 by segment 2122, is then coupled tonode 2104 by segment 2123, and is then coupled to node 2105 by segment2124. In other words, fabric circuits (e.g., 2001) in cooperation withcoupling segments (e.g., 2021) at each node: (a) couple signals receivedfrom the node one position counter-clockwise (e.g., M1 for minus one) tothe path that extends three segments clockwise (e.g., P3 for plusthree); (b) couple signals received from the node two positionscounter-clockwise (M2) to the path that extends two segments clockwise(P2); (c) couple signals received from the node three positionscounter-clockwise (M3) to the path that extends one segment clockwise(P1); (d) couple signals received from the node four positionscounter-clockwise (M4) to the PIOC at this node; and (e) couple thesignal provided by the PIOC at this node to the path that extends threefour segments clockwise (P4).

[0268] In another implementation of fabric 213, fabric 2200 of FIG. 22provides full mesh communication between all ports at each of threefabric nodes. Fabric 2200 includes three circuits 2201-2203 (one at eachfabric node), each having port I/O circuitry (PIOC) that may beidentical to the PIOCs discussed with reference to FIG. 21 except thatfabric circuits (e.g., 2201) in cooperation with coupling segments ateach node: (a) couple signals received from the node one positioncounter-clockwise (M1) to the path that extends one segment clockwise(P1); (b) couple signals received from the node two positionscounter-clockwise (M2) to the PIOC at this node; and (c) couple thesignal provided by the PIOC at this node to the path that extends twosegments clockwise (P2).

[0269] The same physical printed circuit layout (not shown) may be usedfor both fabrics 2100 and 2200. In fabric 2200 segments may be connectedby fillers 2204-2205 across unfilled fabric node positions. Fabric 2200may be upgraded to fabric 2100 by replacing fillers 2204-2205 withfabric circuits 2104-2105 and reconfiguring switching functions offabric circuits 2201-2203 to provide the functions of fabric circuits2101-2103. Such reconfiguration is preferably accomplished by inputs toeach fabric circuit; each fabric circuit being of an identical typehaving internal configuration functions responsive to these inputs.

[0270] Router 102 may include a fabric of the type described above withreference to FIGS. 21 and 22. In one implementation, each port logiccircuit (e.g., 1186, 1188) includes a distributing circuit havingsegment signal switching functions as discussed above. For example,distributing circuit 1402 of FIGS. 14 and 23, provides suitable couplingthrough port logic circuit 1186 so that port logic circuit 1186 may beinstalled in any position of a fabric having any number of populatedpositions (up to a predetermined maximum number of positions).Distribution circuit 1402 includes controller 2301, receivers 2305,interconnecting switch 2306, transmitters 2308, scrambler 2322,descrambler 2324, normalizing switch 2310, and back pressure logic 2312.

[0271] A controller establishes a switch configuration and segmenttermination suitable for a particular under population and total numberof fabric nodes of the fabric. For example, controller 2301 (comprisingcombinatorial logic) receives TOTAL_NODES signal 2302, UNDER_POPULATIONsignal 2303 that indicates the number of positions counter clockwise ofthe present position that are occupied by fillers, and POSITION signal2304 that identifies which fabric node is associated with thisdistributing circuit (e.g., 2101, or 2102, or 2103, and so on).TOTAL_NODES, UNDER_POPULATION, and POSITION signals may each comprise abinary value having several known logic levels each provided through aprinted circuit board trace, a jumper, a manual switch, or an EPM orother memory output. A controller 2301 that receives a non-zero valuefrom the UNDER_POPULATION signal 2303 directs receivers 2305 to use asuitable impedance matching termination circuit. Controller 2302operates interconnecting switch 2306, operates normalizing switch 2310,and configures back pressure logic 2312 in accordance with TOTAL_NODESsignal 2302 and POSITION signal 2304. Typically, operations of switches2306 and 2310 and configuration of backpressure logic 2312 occur duringinitialization of router 102 and initial settings are not changed duringnormal operation of router 102.

[0272] Receivers 2305 include an independent receiver circuit for eachsegment. In other words, each segment is a point to point conductor withno branches so as to simplify high frequency tuning of the conductor andmatching of one transmitter to one receiver for each segment. Receiversreceive signals RING-IN 1170 from segments of the fabric. For example,signal M1 is received by a first receiver, signal M2 by a secondreceiver, and so on. Each receiver may include a phase locked loop forclock and data recovery from the signal received from a segment.Demodulation of the signal received from a segment may include anyconventional demodulation technique (e.g., demodulation of phase shiftkeying).

[0273] Prior to transmission, data to be transmitted may be scrambled sothat energy conveyed by the transmitted signal is distributed amongfrequencies and/or frequency bands. By distributing transmitted energy,noise immunity of the fabric is improved and noise radiation by thefabric is easier to control. Scrambler 2322 provides a scrambled signalon line 2323 in accordance with DATA signal 1434 from dequeue logic 1412associated with this distributing circuit 1402.

[0274] Interconnecting switch 2306 couples each selected signal ofsignals 2307 to a suitable transmitter 2308. Signal selection andcoupling is accomplished in accordance with control signals receivedfrom controller 2301 and in accordance with the fabric architecturediscussed above with reference to FIGS. 21 and 22. Signals on lines 2307include demodulated signals from receivers 2305 and the scrambled datasignal on line 2323. Switch output signals on lines 2309 are coupled totransmitters 2308.

[0275] Transmitters 2308 provide signals RING-O 1172 to segments of thefabric. Transmitters 2308 include an independent transmitter circuit foreach segment. For example, signal M1 of signal group 2309 is transmittedby a first transmitter to provide signal P3 for a first segment, signalM2 of signal group 2309 is transmitted by a second transmitter toprovide signal P2 for a second segment, and so on. Each transmitter mayinclude clock generation circuitry to train the corresponding receiver.Modulation of the signal to be transmitted on a segment may include anyconventional modulation technique (e.g., phase shift keying).

[0276] Descrambler 2324 accepts signals from receivers 2305 andindependently descrambles each signal to provide corresponding cleardata signals on lines 2311. Signals on lines 2311 are provided tonormalizing switch 2310 and to back pressure logic 2312.

[0277] Normalizing switch 2310 provides outputs A-E on data lines 1430to egress buffer 1414 associated with this distributing circuit 1402.The routing of signals received on normalizing switch inputs 0-4 tooutput A-E is directed by controller 2301 so that adjustments (if any)in routing methods performed by frame processor 1424 to account fordifferences in the installed position of port logic circuit 1186 or thetotal number of fabric nodes are simplified.

[0278] Back pressure logic 2312 receives clear data signals 2311 thatmay include back pressure messages transmitted in response to status ofan egress buffer coupled to any fabric node (e.g., from any port logiccircuit of routing circuits 1150-1152). In addition, back pressure logicmay receive CONTROL signals on line 1432 from egress buffer 1414associated with this distributing circuit 1402. Back pressure logic 2312provides CONTROL signals on line 1436 to VOQC 1428 associated with thisdistributing circuit 1402. VOQC responds to CONTROL signals on line 1436to stall or restart any one or more virtual output queues. In oneimplementation VOQC 1428 receives an independent signal from backpressure logic 2312 corresponding to each virtual output queue (e.g.,one VOQ per tuple of physical output port, physical input port, andtraffic class). By forming the egress buffer and distributing circuit onone substrate, a large number of wired signal connections (e.g., for“go” signals from each buffer queue to back pressure logic) areeconomically and reliably implemented.

[0279] In one implementation, each segment is served by a plurality ofchannels (e.g., four to achieve a data rate up to four times the datarate of one channel). The arbitration circuit for a virtual output queuemay place a frame onto a selected one of the four channels. In analternate implementation each channel has an arbitration circuit thatserves virtual output queues (e.g., seventy two queues being fourtraffic classes times eighteen source port identifiers). A particularvirtual output queue may be served by more than one arbitration circuit.

[0280] Routing information may be stored local to one routing processorand messages to be routed using that information may be routed fromother routing processors via the fabric to that routing processor. Forexample, router 105 of FIG. 24 includes routing processors 2402 and 2404each as discussed above with reference to routing processor 1161. Eachprocessor has access to memory for a virtual context table not used bythe other processor. Routing processor 2402 includes memory for virtualcontext table 2403; and, routing processor 2404 includes memory forvirtual context table 2405. Virtual context tables (VCT) 2403 and 2405may be stored in memory on the same integrated circuit substrate as therespective routing processor (e.g., an integrated circuit implementationof a port logic circuit) or may be stored in a memory circuit havingareas reserved for access by each processor (e.g., portions of memorycircuit 1162 as discussed above with reference to Table 12). Routingprocessors 2402 and 2404 route packets via fabric 2406 (e.g., asdiscussed above with reference to fabric 213) using a fabric frame thatencloses the frame used on network 101. The enclosing fabric frameheader may include a designation indicating one of the following:(type 1) the receiving routing processor is to perform no framemodification; (type 2) the receiving routing processor is to performvirtual to nonvirtual frame modification; or (type 3) the receivingrouting processor is to perform nonvirtual to virtual framemodification. The frame modifications for types 2 and 3 above areperformed in the egress buffer of the receiving processor before theframe is transmitted onto network 101.

[0281] Use of fabric frame headers as discussed above is described by aseries of messages 2400 of FIG. 24 that includes routing of virtual R/WI/Os to nonvirtual R/W I/Os and vice versa as discussed above, forexample, with reference to FIGS. 6-11, 13, 14, and 16-20. In messagesequences 2400 member 116 reads and writes a portion of a virtualresource implemented as nonvirtual resource 177 or member 115 (all ofFIG. 1). A transaction that includes an FCP_CMND sequence 2410, one ormore pairs of FCP_XFER_RDY and RD_DATA sequences 2420 and 2440, and anFCP_RSP sequence 2450 accomplish a read transfer of data from nonvirtualresource 177 to member 116. A transaction that includes an FCP_CMNDsequence 2410, one or more pairs of FCP_XFER_RDY and WR_DATA sequences2420 and 2430, and an FCP_RSP sequence 2450 accomplish a write transferof data from member 116 to nonvirtual resource 177. Messages “A” at time2411, “F” at time 2423, “G” at time 2431, “L” at time 2443, and “O” attime 2453 convey no identity of the nonvirtual entity on which the readand write operations occur. Messages “C” at time 2413, “D” at time 2421,“I” at time 2433, “J” at time 2441, and “M” at time 2451 appear to theresource as nonvirtual network traffic with no indication (other thanthe network address of the proxy) that the initiator is a proxy asopposed to a nonvirtual member. Field values used in routing messages ofseries 2400 are described in Tables 22 and 23.

[0282] When VCT 2403 has routing information for the transactionidentified in message “A” at time 2411 as a virtual transaction frommember 116 in FCP_CMND 2410, messages “B” at time 2412 and “H” at time2432 are marked by routing processor 2402 as type 1. Routing processor2404 in its egress buffer (e.g., 1414) removes the marking and passesthe payload as messages “C” at time 2413 and “I” at time 2433.

[0283] When VCT 2405 does not have routing information for the virtualtransaction of message “A”, routing processor 2404 marks messages “E” attime 2422, “K” at time 2442, and “N” at time 2452 as type 3 (e.g.,1730). In response, routing processor 2402 performs modification to eachframe in its egress buffer (e.g., 1910).

[0284] In an alternate configuration wherein VCT 2405 has routinginformation for the transaction identified in. message “A” at time 2411as a virtual transaction and VCT 2403 does not, routing processor 2402marks messages “B” and “H” as type 2 and receives messages “E”, “K”, and“N” marked by routing processor 2404 as type 1. The processing burden ofperforming frame modifications in ingress and egress buffers may beallocated by an administrating process (e.g., managing virtualization).Allocation and reallocation may be accomplished as discussed above withreference to flags returned from a virtual flow lookup in Table 11.TABLE 22 Field Values Mes- LUN and sage Frame Type S_ID D_ID OX_ID RX_IDLBA A FCP_CMND I VM IX — VR B VM T PX — NR C VM T PX — NR D FCP_XFER_(—)T VM PX TX — E RDY T VM PX TX — F VM I IX PX — G WR_DATA I VM IX PX — HVM T PX TX — I VM T PX TX — J RD_DATA T VM PX TX — K T VM PX TX — L VM IIX PX — M FCP_RSP T VM PX TX — N T VM PX TX — O VM I IX PX —

[0285] TABLE 23 Field Value Meaning Assigned By Description I Initiatornetwork port Manufacturer of the WWPN for initiator (e.g., 167).identifier Initiator system T Target network port Administration WWPNfor target (e.g., 115). identifier VM Virtual member Administration whenA network port identifier identifier designing zones intercepted by arouter operating according to various aspects of the present invention.For example, an address in a range of addresses that are reserved fordesignating the router. VR Virtual resource Administration when Aresource logical unit identifier identifier designing zones (e.g., LUN)that has no corresponding physical entity. NR Nonvirtual resourceManufacturer of the WWPN for actual LUN (e.g., 177). identifier Targetsystem IX Initiator's transaction Initiator Any transaction identifiernot identifier currently associated with this initiator. TX Target'sexchange Target Any transaction identifier not identifier currentlyassociated with this target. PX Proxy's exchange Routing processor Anytransaction identifier not identifier currently associated with thisproxy.

[0286] The foregoing description discusses preferred embodiments of thepresent invention which may be changed or modified without departingfrom the scope of the present invention as defined in the claims. Whilefor the sake of clarity of description, several specific embodiments ofthe invention have been described, the scope of the invention isintended to be measured by the claims as set forth below.

What is claimed is:
 41. A method performed by a router for routingframes in a network, the router comprising a managing processor forperforming a proxy process; a plurality of routing processors coupled bya fabric for routing frames to another routing processor of theplurality via the fabric; each routing processor comprising ports forreceiving frames from the network and for routing frames to the network;the method comprising: a step for receiving at a first routing processora first frame from the network; a step for determining at the firstrouting processor that the first frame is part of a virtual controltransaction; a step for routing at least a portion of the virtualcontrol transaction from the first routing processor to a second routingprocessor via the fabric; a step for routing the portion of the virtualcontrol transaction from the second routing processor to the proxyprocess via a link, the managing processor being coupled by the link toa port of the second routing processor; a step for receiving at thefirst routing processor a second frame from the network; a step fordetermining at the first routing processor that the second frame is partof a data transaction; a step for routing at least a portion of the datatransaction from the first routing processor to a nonvirtual destinationwithout cooperation of the proxy.
 42. The method of claim 41 wherein thesecond frame is part of a virtual data transaction and the methodfurther comprises a step for redirecting a frame of the virtual datatransaction to the nonvirtual destination.
 43. The method of claim 42wherein the second frame comprises a virtual transaction identifier thatidentifies at least one of a virtual participant, a virtual member, avirtual resource, a virtual device, a virtual address, a virtual page,and a virtual sector.
 44. The method of claim 42 wherein the secondframe does not include a resource identifier and the step forredirecting comprises: a step for recalling a nonvirtual resourceidentifier; and a step for redirecting in accordance with the nonvirtualresource identifier.
 45. The method of claim 44 wherein the nonvirtualresource identifier identifies at least one of a nonvirtual participant,a nonvirtual device, a nonvirtual address, a nonvirtual page, and anonvirtual sector.
 46. The method of claim 42 wherein the step forredirecting comprises at least one of: a step for rewriting a sourceidentifier; and a step for rewriting a destination identifier.
 47. Amethod performed by a router for routing frames in a network, the routercomprising a managing processor for performing a proxy process; aplurality of routing processors coupled by a fabric; each routingprocessor having a plurality of ports for receiving frames from thenetwork and for routing frames to the network, the method performed byeach routing processor of the plurality, the method comprising: a stepfor receiving at a first routing processor a first frame from thenetwork; a step for determining at the first routing processor that thefirst frame is part of a virtual data transaction that refers to a pagehaving a boundary; a step for determining at the first routing processorwhether data of the virtual data transaction crosses the boundary; andif it is determined that data crosses, a step for routing at least aportion of the virtual data transaction to the proxy via the fabric andvia a link, the managing processor coupled via the link to a port of asecond routing processor.
 48. The method of claim 47 further comprising:a step for routing from the proxy via the link at least a frame of anonvirtual data transaction to accomplish a purpose of the virtual datatransaction; a step for receiving the frame of the nonvirtual datatransaction at the second routing processor; and a step for routing theframe of the nonvirtual data transaction from the second routingprocessor to a nonvirtual entity via the network.
 49. The method ofclaim 47 further comprising: if it is determined that the data does notcross, a step for conducting a nonvirtual data transaction via thenetwork to accomplish a purpose of the virtual data transaction.
 50. Themethod of claim 49 wherein the step of conducting comprises: a step forreceiving from the fabric at a second routing processor a portion of thevirtual data transaction; a step for redirecting at the second routingprocessor a frame of the virtual data transaction to a nonvirtual entityof the nonvirtual data transaction.
 51. The method of claim 49 whereinthe step for redirecting comprises at least one of: a step for rewritinga source identifier; and a step for rewriting a destination identifier.52. A method performed by a router for routing frames in a network therouter comprising a managing processor for performing a proxy process; aplurality of routing processors coupled by a fabric; each routingprocessor having a plurality of ports for receiving frames from thenetwork and for routing frames to the network, the method comprising: astep for receiving at the managing processor from an administratingprocessor via a link routing information comprising a first network portidentifier and a second network port identifier, the managing processorbeing coupled to a port of a first routing processor of the pluralityvia the link; a step for receiving at a second routing processor fromthe managing processor the first network port identifier and the secondnetwork port identifier; a step for routing a frame of a virtual controltransaction from the second routing processor to the managing processorvia the link in accordance with the first network port identifier; and astep for routing a frame of a virtual data transaction comprising thefirst network port identifier from the second routing processor to anonvirtual entity via the network in accordance with the second networkport identifier.
 53. The method of claim 52 wherein the first networkport identifier identifies a proxy process performed by the managingprocessor.
 54. The method of claim 52 wherein: the router furthercomprises a memory circuit and a supervising processor coupled for datacommunication between the managing processor and the memory circuit,each routing processor of the plurality of routing processors havingaccess to the memory circuit; the step for receiving at the secondrouting processor comprises: a step for storing the first network portidentifier and the second network port identifier in the memory circuitvia the supervising processor; and a step for accessing the firstnetwork port identifier and the second network port identifier from thememory circuit.
 55. A method performed by a router for routing frames ina network the router comprising a managing processor; and a plurality ofrouting processors coupled by a fabric; each routing processor having aplurality of ports for receiving frames from the network and for routingframes to the network, method comprising: a step for receiving a firstframe at a first routing processor of the plurality from the network; afirst step for routing at least a portion of the first frame from thefirst routing processor to the network; a second step for routing atleast a portion of the first frame from the first routing processor tothe managing processor via the fabric, a second routing processor of theplurality, and a link, the managing processor being coupled by the linkto a port of the second routing processor.
 56. The method of claim 55further comprising a step for maintaining a cache at the managingprocessor in accordance with the received portion of the first frame.57. The method of claim 55 further comprising a step for maintaining amirror at the managing processor in accordance with the received portionof the first frame.
 58. A method performed by a router for routingframes in a network the router comprising a managing processor; and aplurality of routing processors coupled by a fabric; each routingprocessor having a plurality of ports for receiving frames from thenetwork and for routing frames to the network, method comprising: a stepfor receiving a first frame at a first routing processor of theplurality from the network; a step for accumulating at the first routingprocessor a count in accordance with receiving the first frame; a stepfor routing the count from the first routing processor to the managingprocessor via the fabric, a second routing processor of the plurality,and a link, the managing processor being coupled by the link to a portof the second routing processor.
 59. The method of claim 58 furthercomprising a step for reporting a network traffic statistic at themanaging processor in accordance with the received portion of the firstframe.
 60. A router for routing frames in a network, the routercomprising: means for performing a proxy process; a plurality of routingmeans for receiving frames from the network and for routing frames tothe network, each routing means comprising ports; distributing means forrouting frames between routing means of the plurality; means forreceiving at a first routing means a first frame from the network; meansfor determining at the first routing means that the first frame is partof a virtual control transaction; means for routing at least a portionof the virtual control transaction from the first routing means to asecond routing means via the distributing means; means for routing theportion of the virtual control transaction from the second routing meansto the proxy process via a link, the managing means being coupled by thelink to a port of the second routing means; means for receiving at thefirst routing means a second frame from the network; means fordetermining at the first routing means that the second frame is part ofa data transaction; and means for routing at least a portion of the datatransaction from the first routing means to a nonvirtual destinationwithout cooperation of the proxy process.
 61. The router of claim 60wherein the second frame is part of a virtual data transaction and therouter further comprises means for redirecting a frame of the virtualdata transaction to the nonvirtual destination.
 62. The router of claim61 wherein the second frame comprises a virtual transaction identifierthat identifies at least one of a virtual participant, a virtual member,a virtual resource, a virtual device, a virtual address, a virtual page,and a virtual sector.
 63. The router of claim 61 wherein: the secondframe does not include a resource identifier; the means for redirectingcomprises means for recalling a nonvirtual resource identifier; and themeans for redirecting redirects in further accordance with thenonvirtual resource identifier.
 64. The router of claim 63 wherein thenonvirtual resource identifier identifies at least one of a nonvirtualparticipant, a nonvirtual device, a nonvirtual address, a nonvirtualpage, and a nonvirtual sector.
 65. The router of claim 61 wherein themeans for redirecting comprises at least one of: means for rewriting asource identifier; and means for rewriting a destination identifier. 66.A router for routing frames in a network, the router comprising: amanaging means for performing a proxy process; a plurality of routingmeans for receiving frames from the network and for routing frames tothe network, each routing means having a plurality of ports;distributing means for routing frames between routing means of theplurality; means for receiving at a first routing means a first framefrom the network; means for determining at the first routing means thatthe first frame is part of a virtual data transaction that refers to apage having a boundary; means for determining at the first routing meanswhether data of the virtual data transaction crosses the boundary; andmeans for routing, responsive to a determination that data crosses, atleast a portion of the virtual data transaction to the proxy via thedistributing means and via a link, the managing means coupled via thelink to a port of a second routing means.
 67. The router of claim 66further comprising: means for routing from the proxy via the link atleast a frame of a nonvirtual data transaction to accomplish a purposeof the virtual data transaction; means for receiving the frame of thenonvirtual data transaction at the second routing means; and means forrouting the frame of the nonvirtual data transaction from the secondrouting means to a nonvirtual entity via the network.
 68. The router ofclaim 66 further comprising: means for conducting, responsive to adetermination that the data does not cross, a nonvirtual datatransaction via the network to accomplish a purpose of the virtual datatransaction.
 69. The router of claim 68 wherein the means of conductingcomprises: means for receiving from the distributing means at a secondrouting means a portion of the virtual data transaction; means forredirecting at the second routing means a frame of the virtual datatransaction to a nonvirtual entity of the nonvirtual data transaction.70. The router of claim 68 wherein the means for redirecting comprisesat least one of: means for rewriting a source identifier; and means forrewriting a destination identifier.
 71. A router for routing frames in anetwork the router comprising: a managing means for performing a proxyprocess; a plurality of routing means for receiving frames from thenetwork and for routing frames to the network, each routing means havinga plurality of ports; a distributing means for routing frames betweenrouting means of the plurality; means for receiving at the managingmeans from an administrating means via a link routing informationcomprising a first network port identifier and a second network portidentifier, the managing means being coupled to a port of a firstrouting means of the plurality via the link; means for receiving at asecond routing means from the managing means the first network portidentifier and the second network port identifier; means for routing aframe of a virtual control transaction from the second routing means tothe managing means via the link in accordance with the first networkport identifier; and means for routing a frame of a virtual datatransaction comprising the first network port identifier from the secondrouting means to a nonvirtual entity via the network in accordance withthe second network port identifier.
 72. The router of claim 71 whereinthe first network port identifier identifies a proxy process performedby the managing means.
 73. The router of claim 71 wherein: the routerfurther comprises a memory circuit and a supervising means forcommunicating between the managing means and the memory circuit, eachrouting means of the plurality of routing means having access to thememory circuit; the means for receiving at the second routing meanscomprises: means for storing the first network port identifier and thesecond network port identifier in the memory circuit via the supervisingmeans; and means for accessing the first network port identifier and thesecond network port identifier from the memory circuit.
 74. A router forrouting frames in a network, the router comprising: a managing means forreceiving a payload of a virtual control frame and for forming acorresponding nonvirtual control frame; a plurality of routing means forreceiving frames from the network and for routing frames to the network,each routing means having a plurality of ports; the pluralitycomprising: a first routing means for receiving the virtual controlframe from the network; and a second routing means; distributing meansfor routing frames between routing means of the plurality, the payloadof the virtual control frame being routed by the distributing means fromthe first routing means to the second routing means; wherein themanaging means receives the payload from the second routing means via alink to a port of the second routing means and sends the nonvirtualcontrol frame to the second routing means via the link; and wherein thesecond routing means routes a payload of the nonvirtual control frame.75. The router of claim 74 wherein: each routing means comprises meansfor providing a network traffic statistic; and the managing meansfurther comprises means for reporting in accordance with respectiveprovided network traffic statistics routed to the managing means via thedistributing means, the second routing means, and the link.
 76. Therouter of claim 74 wherein the network traffic statistic comprises aportion of a frame received by a routing means of the plurality.
 77. Therouter of claim 74 wherein ech routing means further comprises means foraccumulating a respective count and the network traffic statistic isprovided in accordance with the count.
 78. The router of claim 74wherein: each routing means provides to the managing means via thedistributing means, the second routing means, and the link respectivepayloads of frames of first transactions in a first frame sequencereceived from the network; and the managing means further comprises:means for storing in a cache for each transaction the respectivepayloads; and means for providing the respective payloads in secondtransactions in a second sequence different from the first sequence,providing being via the link, the second routing means, and thedistributing means.
 79. The router of claim 74 wherein: each routingmeans provides to the managing means via the distributing means, thesecond routing means, and the link a copy of respective payloads offrames of first transactions received from the network for writing to astorage resource; the managing means further comprises means formirroring the payloads in second transactions directed to a mirrorstorage resource, wherein copies and second transactions arecommunicated between the routing means and the managing means via thelink, the second routing means, and the distributing means.
 80. Therouter of claim 74 wherein: each routing means provides to the managingmeans via the distributing means, the second routing means, and the linkpayloads of frames of first transactions received from the network forwriting to a storage resource; and means for maintaining a snapshot ofthe storage resource prior to writing to the storage resource,maintaining accomplished with frames of second transactions formed inaccordance with the payloads, wherein the payloads and secondtransactions are communicated between the routing means and the managingmeans via the link, the second routing means, and the distributingmeans.